# Linking 2 leisure batteries??



## chrishunter (Jan 11, 2021)

My idea is to link 2 leisure batteries, by drilling a cable size hole in the battery compartment making it a tight fit.Feeding 2core cable through to the compartment under the back seat {compass avantgarde 200} to the other leisure battery. Now the questions are what size cable to use would 2 core 1.5mm do it, will the alternator be able to charge all 3 batteries and am I correct in  wiring the positive terminal to the negative second battery and the negative to positive on the spare battery.


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## wildebus (Jan 11, 2021)

1.5mm cable?   Absolutely not!  nowhere near close.
Your suggestion/thoughts on how to cable is very wrong as well.

Sorry to say this, but I don't think you have enough knowledge to tackle this job.


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## clarkpeacock (Jan 11, 2021)

Agree with Wildebus.


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## colinm (Jan 11, 2021)

wildebus said:


> 1.5mm cable?   Absolutely not!  nowhere near close.
> Your suggestion/thoughts on how to cable is very wrong as well.
> 
> Sorry to say this, but I don't think you have enough knowledge to tackle this job.


As this, you appear to be so far from being correct I don't feel it right to give instructions via posts on this this forum.


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## n brown (Jan 11, 2021)

hate to say this ,but everything you describe is a recipe for a burnt out van at best .


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## chrishunter (Jan 11, 2021)

wildebus said:


> 1.5mm cable?   Absolutely not!  nowhere near close.
> Your suggestion/thoughts on how to cable is very wrong as well.
> 
> Sorry to say this, but I don't think you have enough knowledge to tackle this job.


sorry that should have been pos to pos and neg to neg ,could I use 2.5 cable


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## trevskoda (Jan 11, 2021)

Its done like this using proper battery cable & clamps which can be bought at any good car shop, do get someone else to do the job.


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## chrishunter (Jan 11, 2021)

trevskoda said:


> Its done like this using proper battery cable & clamps which can be bought at any good car shop, do get someone else to do the job.View attachment 91033


I THINK I`LL CARRY ON SWOPPING THE BATTERIES OVER WHEN I`M AWAY..THOUGHT IT MIGHT SAVE MY BACK..


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## trevskoda (Jan 11, 2021)

chrishunter said:


> I THINK I`LL CARRY ON SWOPPING THE BATTERIES OVER WHEN I`M AWAY..THOUGHT IT MIGHT SAVE MY BACK..


A garage could do this in an hr for you, have you no solar or is the engine not charging the battery, as a rule 200ah of batts is required to wild camp for a full 24 hr day max.


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## Robmac (Jan 11, 2021)

trevskoda said:


> A garage could do this in an hr for you, have you no solar or is the engine not charging the battery, *as a rule 200ah of batts is required to wild camp for a full 24 hr day max.*



I wouldn't go that far Trev.

My first camper didn't even have a leisure battery!


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## trevskoda (Jan 11, 2021)

Robmac said:


> I wouldn't go that far Trev.
> 
> My first camper didn't even have a leisure battery!


That was in the dark ages.


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## Robmac (Jan 11, 2021)

trevskoda said:


> That was in the dark ages.



Correct Trev, in more ways than one!


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## trevskoda (Jan 11, 2021)

Robmac said:


> Correct Trev, in more ways than one!


Once you have a few to many beers the lights go out anyway.


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## chrishunter (Jan 11, 2021)

trevskoda said:


> A garage could do this in an hr for you, have you no solar or is the engine not charging the battery, as a rule 200ah of batts is required to wild camp for a full 24 hr day max.


I don't have solar ,and i`ve just had a new alternator fitted.when I do a check under the bonnet I always check the battery and the charge with a meter..


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## trevskoda (Jan 11, 2021)

chrishunter said:


> I don't have solar ,and i`ve just had a new alternator fitted.when I do a check under the bonnet I always check the battery and the charge with a meter..


Solar is a requirement these days for the loads and charging when you have stopped, something you should be looking into as summer will be here soon.


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## 1 Cup (Jan 11, 2021)

The amps you draw is how thick the jump wire should be.
You can just use 
The cable I use for my old van. I got from scrap yard including terminals cut straight from under bonnet off any car, 13 or 10 mm spanner used to remove terminals from battery before I cut cables


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## molly 2 (Jan 12, 2021)

Robmac said:


> Correct Trev, in more ways than one!


Was that the dark ages or the good old days


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## molly 2 (Jan 12, 2021)

You can buy different lengths  of ready  made
Battery cables from  halfords


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## Robmac (Jan 12, 2021)

trevskoda said:


> Once you have a few to many beers the lights go out anyway.



The voice of experience Trev?

You want to cut down a bit mate.


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## Tookey (Jan 12, 2021)

Hi Chris,

Like you I am a novice and after your first post understand why those that are knowledgeable are now hesitant to give advice.  Can I suggest doing your own research on youtube and then coming back here and asking for confirmation that what you've figured out will work, is safe and then do the project.

Some replies do seem brutal but that is only cos nobody wants you stuck in a moho on fire


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## Fisherman (Jan 12, 2021)

I have been watching this thread, and quite frankly it scares the S—t out of me.
I brings back memories of a neighbour who was about to wire up a 10.5 kw shower with some 1.5mm cable he had in his garage.

Chris this is a simple job for someone who knows what they are doing, you don’t.
I would seriously advise you not to mess about with electricity. But if you do insist take a look at this. Take my advice listen to wildebus, I do. Take care, be really careful.








						Caravan, Motorhome, Camper 12v Pre Wired Leisure Battery Clamps & Cable  - PO935 5060070219370 | eBay
					

A & L Leisure.



					www.ebay.co.uk


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## harrow (Jan 12, 2021)

Where I used to work we had huge solid copper busbars 8 inches by 2 inches some were doubled up.

But we have to live in a real world, why use 2 cables ?


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## colinm (Jan 12, 2021)

harrow said:


> But we have to live in a real world, why use 2 cables ?



See post 7


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## molly 2 (Jan 12, 2021)

Fisherman said:


> I have been watching this thread, and quite frankly it scares the S—t out of me.
> I brings back memories of a neighbour who was about to wire up a 10.5 kw shower with some 1.5mm cable he had in his garage.
> 
> Chris this is a simple job for someone who knows what they are doing, you don’t.
> ...


These cables  look to thin you need cables  like short jump   leads


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## chrishunter (Jan 12, 2021)

Tookey said:


> Hi Chris,
> 
> Like you I am a novice and after your first post understand why those that are knowledgeable are now hesitant to give advice.  Can I suggest doing your own research on youtube and then coming back here and asking for confirmation that what you've figured out will work, is safe and then do the project.
> 
> Some replies do seem brutal but that is only cos nobody wants you stuck in a moho on fire


yes your right..


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## molly 2 (Jan 12, 2021)

Doing it wrong could be horrendous , follow  trevs Drawing .look on you tube lots of advice ,iinstructions,


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## Fisherman (Jan 12, 2021)

molly 2 said:


> These cables  look to thin you need cables  like short jump   leads



I would reckon 10mm would be required, I am sure wildebus would know.

To be honest I never really looked at the photos, I assumed as this is supposed to be for a Motorhome it would be fine, but looking at the photos I would agree, they look to thin.


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## wildebus (Jan 12, 2021)

trevskoda said:


> Its done like this using proper battery cable & clamps which can be bought at any good car shop, do get someone else to do the job.


That's the way to cable up.  In terms of cable length, equal gauge & length cables (to give equal resistance) are advised BETWEEN the batteries, but once out of the battery bank, equal length is not a factor as far as I am concerned, so the note above about equal length cables in the picture at the "To +12V" and "To Ground" point is not relevant (IMO)

Additional advice ....
If the batteries are separated by any significant distance then you need to incorporate fuses into the inter-battery wiring to protect against shorting (with two batteries there are two sources of energy remember and so both sources need protected from/against )
Cable size, I would usually not go below 16mm2 cable generally and quite possibly higher if there is any likelyhood of high current draws (say from an inverter).
Some people add more batteries for longer off-grid time; some people add more batteries to allow them to have more power.  If it is the latter, beefier cables are definately needed.  The Battery interconnects  (between the three batteries) on my Campervan were 50mm2 in order to allow a 2400W inverter to be used reliably.


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## wildebus (Jan 12, 2021)

Fisherman said:


> I would reckon 10mm would be required, I am sure wildebus would know.
> 
> To be honest I never really looked at the photos, I assumed as this is supposed to be for a Motorhome it would be fine, but looking at the photos I would agree, they look to thin.


In the link you posted to those cables, they initially looked fine.  But when you look closer (which I did following a couple of comments), it looks like the cables are around 4mm (guessing here) and have some sheathing over them which I am sure is not the intent but makes them appear much thicker.


Also there have been some comments about using Jump Lead Cables.  Generally they are not good enough either.  You might think if they are ok for jumping a engine they must be pretty hefty and they look good and thick?  Well, the typical jump lead cable is actually not very good at jumping an engine and if you feel one after being used they can be pretty warm!  and you feed that heat despite the insulation on them usually being twice as thick as proper cables  (which is why they LOOK thick but are not in reality when it comes to the central core.

Best cable to get is generally UK/European (NOT Chinese) made Welding Cable.  It is flexible and high quality and not expensive for the amount of cable that is required.
If anyone has bought a Far East supplied Inverter which comes with cables, they will know why I have said "NOT Chinese" when it comes to Cable!


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## molly 2 (Jan 12, 2021)

My comment on jump  leads was for the physical  size  ,not a recommendation  ,.awg and mm2 can be confusing


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## r4dent (Jan 12, 2021)

Easiest solution is to fit a bigger capacity battery.  
When fitting two they should be same age/ make & model/ capacity so buy a big one instead of.s two identical smaller ones.
Cable size required depends on length of cable runs and acceptable voltage drop.

If determined to go to 2 batteries I support those who believe you need to find an auto electrician. 

For either 1 bigger or 2 batteries you check the charger is us up to it. 

This is a must read http://www.WEBSITE BLOCKED BY ADMIN/add-a-second-battery.php


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## trevskoda (Jan 12, 2021)

My batteries are about 6 feet apart and fuses ar both ends, one is in the passengers footwell & the other is in a locker where the sink pump and heater are half way down the van.
Follow wildbuses advice and dont let any tom dick or harry poke at the wiring.


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## SimonM (Jan 12, 2021)

Look at what you end up with if you think you know what you’re doing


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## Robmac (Jan 12, 2021)

To be honest, I don't see a problem with the OP doing this himself.

He has taken steps to ask advice here and not just gone ahead and done it, and there is loads of stuff online including diagrams and tutorials to guide him. I would imagine that many of the self builders here are not qualified auto electricians but have wired their vans without endangering themselves. I've done basic wiring myself without knowing much at all, but with help and advice and a bit of double/treble checking I have managed to do it safely. The more complicated stuff I've got a mate on here who helps me out by doing it for me!


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## trevskoda (Jan 12, 2021)

Yes if he is happy then go ahead, if not leave alone.


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## n brown (Jan 12, 2021)

trouble is ,i'm a fervent believer that everyone should have a camper, and a lot of people can only afford to self build . and of those , many can only afford second hand and found/recycled materials . so paying a sparkie or a gas fitter etc might be out of the question. 
as Rob says , the OP has the sense to ask a very valuable source of info ,us , and hasn't been offended by the ,shall we say ,robustness ,of some of the answers ! so ,given that ,let's make sure he's asked all the right questions and been given the most useful answers


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## Fisherman (Jan 12, 2021)

Found this on eBay 









						Battery Lead Power Strap Earth Bond Leisure Cable Leads - 16mm2 - 50mm2 Terminal  | eBay
					

Copper conductor with P.V.C insulation, (resistant to oils, petrol, diesel, lubes and a range of diluted acids). All Leads are Crimped for a solid crimp and connection, then protected in the correct colour heat shrink to match the cable colour.



					www.ebay.co.uk


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## wildebus (Jan 12, 2021)

trevskoda said:


> My batteries are about 6 feet apart and fuses ar both ends, one is in the passengers footwell & the other is in a locker where the sink pump and heater are half way down the van.....


Always best to be safe  
On the installation below, the two batteries were only what? 2 foot apart?  but I still fitted a fuse to each battery as the connecting cables ran along the floor between the bases, as potential for shorting in the case of an accident



Seats Bases by David, on Flickr
(the RHS +VE battery connection shown was temporary  while waiting for the multi-fuse block)

The only time you might not need to fit fuses is if the cables were so short the chance of shorting is near-impossible  (on my current bank, the cables are like that and they wouldn't even reach to an opposite terminal or any ground point to create a problem - but there is still a 'master fuse' for the bank as a precaution)


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## r4dent (Jan 12, 2021)

trevskoda said:


> My batteries are about 6 feet apart and fuses ar both ends, one is in the passengers footwell & the other is in a locker where the sink pump and heater are half way down the van.
> Follow wildbuses advice and dont let any tom dick or harry poke at the wiring.



Are you  talking about two hab batteries connected in parallel which is what the reference to cable size being dependent on distance apart is about

or are you talking about one cab battery (often located in footwell) and one hab battery (usually located in a  locker in habitation area) which are not connected to each other
.
or are you  talking about two batteries connected in parallel which provide both cab & hab services.I've never seen this in a professional build


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## trevskoda (Jan 12, 2021)

r4dent said:


> Are you  talking about two hab batteries connected in parallel which is what the reference to cable size being dependent on distance apart is about
> 
> or are you talking about one cab battery (often located in footwell) and one hab battery (usually located in a  locker in habitation area) which are not connected to each other
> .
> or are you  talking about two batteries connected in parallel which provide both cab & hab services.I've never seen this in a professional build


No two les batteries, truck cam with only one in the footwell and a long cable to run the rear chairlift, I shortened the cable as to connect to a second service batt in a cupboard, from new there was one fuse at diode take of under the bonnet, I now have a second at other end. I also had to do a part rewire of the van as the split diode unit only let 13.7 volts to batts, I now have bypass relays on a switch going round the old unit, but if one fails I will still get a charge.


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## Robmac (Jan 13, 2021)

r4dent said:


> or are you  talking about two batteries connected in parallel which provide both cab & hab services.I've never seen this in a professional build



I've seen this in boats many times and my present boat has such a setup. In fact they make dual purpose batteries for this. But it wouldn't really be suitable for a motorhome.

But the way I read it is that the OP wants to add a second leisure battery in parallel l to the existing one. But I could be wrong.


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## Wooie1958 (Jan 13, 2021)

Robmac said:


> I've seen this in boats many times and my present boat has such a setup. In fact they make dual purpose batteries for this. But it wouldn't really be suitable for a motorhome.
> 
> But the way I read it is that the OP wants to add a second leisure battery in parallel l to the existing one. But I could be wrong.



That`s exactly how i read it as well Rob however it could have been worded better and it`s the last phrase really worries me      

They simply want to add a second leisure battery but it will not be right next to the original so ..............................

1,  What size cable do i need to use to connect the two leisure batteries together ?

2, Is the alterator capable of charging all three batteries, i.e. starter battery and two leisure batteries ?

*Now the worrying bit *

3, How to connect the two leisure batteries together ?

This is the worrying bit, they have got that completely wrong because to keep the voltage at 12 volt they need connecting in parallel and NOT in series.

To keep the system at 12 volts they need connecting in parallel, positive to positive and negative to negative which is correct for the OP`s motorhome

To make the system 24 volt they need connecting in series, positive to negative and negative to positive which is NOT correct for the OP`s motorhome

The OP does not have a clear idea on how to do it so it would be better and more importantly safer if someone else who is qualified does the job for them.

It`s pointless and achieves nothing just having a go at them.


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## Tookey (Jan 13, 2021)

I for one hope Chris gives it a go. One of the best things about this forum is the assistance members will offer to each other. I believe if Chris does he research, presents his plans for scrutiny and then shares some clear photos once completed it can be done correctly. Chris will gain both knowledge and satisfaction and those that helped can give themselves a little pat on the shoulder..........job well done.

Chris can always go 'belt n braces' and show his work to an auto electrician if it will help him sleep better at night.


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## mistericeman (Jan 13, 2021)

Frankly it's a good job some folks actually try to do stuff themselves or this (along with a lot of other forums) 
Would be a very boring read. 

Yes it's important to take advice.... 
BUT it's also important to realise that NONE of us were born experts.... We've all been taught, either by ourselves or others. 

Information and advice are freely given on here and combined with books (remember them) and YouTube videos, all sorts of things are possible.


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## chrishunter (Jan 13, 2021)

Is there a danger of leisure batteries gassing off when charging. I remember when we charged the generator batteries at the hospital when we turned on the charger they were in a sealed room with extractors on. So isnt it dangerous to have the batteries in a cupboard in the van when on charge at night when sleeping.


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## chrishunter (Jan 13, 2021)

just had a look online for a bigger ah battery .problem is I'm limited to the size of the compartment,which is L300 x h220 x w170... I'm trying to make sure I've enough in the leisure battery to last ,we probably go away for a week stopping for 3days ,no hook up. only other thought is 1 leisure battery and buy a solar panel any suggestions..???


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## winks (Jan 13, 2021)

Batteries do give off small amounts of Hydrogen which can easily be vented, usually through the floor of battery housing, using small bore plastic pipe like that used in fish tanks etc. This is lead acid batteries.

As for the choice of battery that 300mm is a bit tight for most on Alpha Batteries and there are choices to be made around technology and budget. I have always found Alpha to be very good value especially with our member discount. There is a load of help available from here with regards to solar and battery management but the basics are, get yourself a good quality MPPT controller. Everyone has their favoured  manufacturers but Victron,  Epever and Votronic are well regarded. Also go for as big a solar panel as you can fit on the roof or carry and stand outside to face the sun which will greatly increase the energy harvested.

A lot to learn but keep asking questions.






						Leisure Battery - Cheap Leisure Batteries - Express Next Day Delivery - Alpha Batteries
					

Order your next Leisure Battery online from Alpha Batteries today! We stock a wide range of Leisure Batteries ready for Express UK Next Day Delivery.




					www.alpha-batteries.co.uk
				




Cheers

H


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## Bigshug (Jan 13, 2021)

Absolutely get a solar panel, if you intend to be off grid for three days, the bigger the better! I would also suggest using a good quality controller, I originally had a Ring combined solar and B2B controller, which was adequate. I later changed to a victron MPPT solar controller and a Sterling B2B charger, and the improvement was amazing!!
 I have just noticed that the Sterling B2B charger now incorporates a solar controller, which when the leisure battery is full diverts a small charge to the vehicle battery.


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## chrishunter (Jan 13, 2021)

Bigshug said:


> Absolutely get a solar panel, if you intend to be off grid for three days, the bigger the better! I would also suggest using a good quality controller, I originally had a Ring combined solar and B2B controller, which was adequate. I later changed to a victron MPPT solar controller and a Sterling B2B charger, and the improvement was amazing!!
> I have just noticed that the Sterling B2B charger now incorporates a solar controller, which when the leisure battery is full diverts a small charge to the vehicle battery.


I think thats the way to go.


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## brian c (Jan 13, 2021)

I agree with mistericeman. Thread 44.   Also not everyone has the ability  through age/ disablement to do the tasks that some people say it’s easy .you just do this then this etc  i for one have learnt a lot reading the threads  . A lot completely lost me .  But still read them. Brian.  The


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## trevskoda (Jan 13, 2021)

I would never buy all in one box, if one bit fails you are stuffed, yoy will at least want 2 100ah batts and 200w solar running through a mppt regulator, go for votronic as there is a take of for the engine battery, good luck.


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## Nabsim (Jan 13, 2021)

chrishunter said:


> just had a look online for a bigger ah battery .problem is I'm limited to the size of the compartment,which is L300 x h220 x w170... I'm trying to make sure I've enough in the leisure battery to last ,we probably go away for a week stopping for 3days ,no hook up. only other thought is 1 leisure battery and buy a solar panel any suggestions..???


Solar is good for so many months of the year so much depends on when you use the van and where you go. Where I am today has been overcast and frequent rain and most I have seen is 4W off 300W of solar panels. Dont confuse charging with storage, if you need two batterys then fit them, you can use solar to get some charge on good days/summer. Of course if all you run are a few led lights then winter may not be a problem for you


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## maingate (Jan 13, 2021)

chrishunter said:


> I THINK I`LL CARRY ON SWOPPING THE BATTERIES OVER WHEN I`M AWAY..THOUGHT IT MIGHT SAVE MY BACK..



You can do what you wanted as long as you connect as shown by Trevskoda. The connecting cable should be fine with 2.5 or 4 mm sq. cable (my second battery was connected by thhee dealer using the official Autotrail kit for the job. The wiring was about 1.5 mm sq with a 30 amp fuse inline on the positive lead. I actually returned it and made them fit something better than 1.5 mm wire).

Remember that you will need a fuse on the positive lead and a vent tube through the floor on the new battery. A 30 amp fuse was (in my opinion overkill). I would fit a 15 or 20 amp fuse myself unless you use a large inverter. If you do use an inverter then your cable size and fuse rating needs ramping right up.


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## clarkpeacock (Jan 13, 2021)

maingate said:


> You can do what you wanted as long as you connect as shown by Trevskoda. The connecting cable should be fine with 2.5 or 4 mm sq. cable (my second battery was connected by thhee dealer using the official Autotrail kit for the job. The wiring was about 1.5 mm sq with a 30 amp fuse inline on the positive lead. I actually returned it and made them fit something better than 1.5 mm wire).
> 
> Remember that you will need a fuse on the positive lead and a vent tube through the floor on the new battery. A 30 amp fuse was (in my opinion overkill). I would fit a 15 or 20 amp fuse myself unless you use a large inverter. If you do use an inverter then your cable size and fuse rating needs ramping right up.



My brother ordered an optional 2nd battery with his brand new Burstner, and this is how the dealer fitted it. To me, the wire seems far too thin, and the take off is from the original battery only. 


. A poor job in my opinion, and an example to the OP of how not to do it!


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## harrow (Jan 13, 2021)

clarkpeacock said:


> My brother ordered an optional 2nd battery with his brand new Burstner, and this is how the dealer fitted it. To me, the wire seems far too thin, and the take off is from the original battery only. View attachment 91118. A poor job in my opinion, and an example to the OP of how not to do it!



I have seen a few of these why are the positive terminal uncovered on the second battery, far more risk.


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## molly 2 (Jan 14, 2021)

Fitting an inverted to above set up could be a disaster


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## chrishunter (Jan 14, 2021)

Nabsim said:


> Solar is good for so many months of the year so much depends on when you use the van and where you go. Where I am today has been overcast and frequent rain and most I have seen is 4W off 300W of solar panels. Dont confuse charging with storage, if you need two batterys then fit them, you can use solar to get some charge on good days/summer. Of course if all you run are a few led lights then winter may not be a problem for you


I'm using led lighting, probably only one on at a time ,and the TV and water pump as required.Got to sort something before getting away hopefully in March , for a week stopping for 2/3 days then moving on ,with no hook up.


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## Brockley (Jan 14, 2021)

chrishunter said:


> I'm using led lighting, probably only one on at a time ,and the TV and water pump as required.Got to sort something before getting away hopefully in March , for a week stopping for 2/3 days then moving on ,with no hook up.



It’s amazing what you can learn from YouTube and from the good folk here (although I’m still waiting for someone to get back to me about my split charger question.. lol). You could always get a competent electrician to check your plan before doing the work yourself and then again before you run anything if you aren’t too sure and still save money.

Victron have a great little tool kit app you can download from the App Store. There is a very easy to use cable calculator included. Just enter dc, 12 volts, length of cable and the current in amps and it will tell you the gauge of cable required in mm squared.

Also and sorry if anyone has already mentioned this, but you could ruin the new battery if doesn’t perfectly match your existing one, especially if the existing one has sulphated and lost full efficiency, one will pull the other down.

I’ve messed with lead acid for too long now. The additional 80amp tilting solar panel and a Victron mppt controller certainly has helped me out a lot, but I’m fed up of having to fettle all the time especially at this time of year so I’ve bitten the bullet and ordered a complete lithium system - 200ah Bluetooth Novel battery, 30 amp Victron  b to b charger, 40 amp Victron mains charger from Quality Source ltd. Just over £2100 all in posted. Seems a lot but should end all worry of battery management for the next ten years. The battery comes with a 2000 cycle guarantee. Should see me out!


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## Glynno (Jan 16, 2021)

clarkpeacock said:


> My brother ordered an optional 2nd battery with his brand new Burstner, and this is how the dealer fitted it. To me, the wire seems far too thin, and the take off is from the original battery only. View attachment 91118. A poor job in my opinion, and an example to the OP of how not to do it!


The patch leads are protected via a 15 amp fuse. Don’t forget the main vehicle battery leads are 16mm to cope with starting loads of 120 amp or so. The leads from the first battery would probably be 10 mm to allow for volt drop over the length. To run a 15 amp load would be quite high as the batteries would be sharing this load. The cables look like about 6 mm which could take a higher amperage than the fuse. Therefore it seems safe and workable. Things are not always as they seem. I hope this helps in your worries.  You can buy loops from eBay that are complete with fusecarrier quite cheaply.
Look at the diagram for above. It shows you how to do it and the types of terminals available And also reminds me that I need a fuse on the positive link. Ooops!
It may be worth investing in battery terminal covers to be safer. These are probably covered by a timber seat cover or such. So are normally not accessible without tools.


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## Glynno (Jan 16, 2021)

molly 2 said:


> You can buy different lengths  of ready  made
> Battery cables from  halfords


Or eBay if you don’t want to go out.


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## badgerdid (Jan 17, 2021)

When I did my self build it used 16mm welding cable from the engine battery to the two leisure battery’s for decent charging and the same cable from the batteries to electric bus bars, worked a treat.


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## Pudsey Bear (Jan 17, 2021)

I linked my two 125ah lbs and my 125ah vb together, I took advise from Peter, (Listerdiesel) he knocked me up a 25mm2 cable and sent a fuse, 25a i think, it worked fine til I sold the van.


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## Jack vdl (Jan 17, 2021)

It really depends on how much current you take out of the batteries.
For instance, do you use an electric kettle or a microwave, or an electric grill?
If not, a 10 or 12 mm2 should do fine.


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## Pudsey Bear (Jan 17, 2021)

Not to argue, but ask a professional, most of what you read on a moho forum will be hearsay.


Admin knows his stuff


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## wildebus (Jan 17, 2021)

Pudsey Bear said:


> Not to argue, but ask a professional, most of what you read on a moho forum will be hearsay.
> 
> 
> Admin knows his stuff


and a lot is herasey as well


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## Tookey (Jan 17, 2021)

Pudsey Bear said:


> Not to argue, but ask a professional, most of what you read on a moho forum will be hearsay.
> 
> 
> Admin knows his stuff


Although this forum is not made up of members doing there first VW conversion, many members have decades of experience and knowledge to share. I believe a combined effort of members here could build a moho from scratch including engine, transmission and chassis

Many could tend the bbq, drink beer and offer moral support as well, myself included


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## wildebus (Jan 17, 2021)

Pudsey Bear said:


> I linked my two 125ah lbs and my 125ah vb together, I took advise from Peter, (Listerdiesel) he knocked me up a 25mm2 cable and sent a fuse, 25a i think, it worked fine til I sold the van.


I think you may have posted up a wiring diagram from Peter as well? That diagram is a good resource for folk to look at as well.

There are two aspects to doing wiring.
1) doing it safely.   That is a minimum and people need to remember that the way a motorhome is built and the wiring used is suitable only for how it was supplied.  As soon as upgrades occur  (bigger batteries, more powerful chargers, inverter additions, etc), that original wiring is likely to no longer to fit for purpose and should not be used as a template on how to install
2)  doing it well.   There is a difference between fitting something and fitting something so it works in the optimum way.  someone can install a second battery with 1mm wiring if they want and as long as they have got suitable fusing in place it will be safe enough, but they will have wasted a lot of their money as they will not get close to the best out of their system.  
The cost of doing it right is rarely much more then doing it badly.


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## Pudsey Bear (Jan 17, 2021)

I don't think I ever did a diagram nor Peter, it was just connecting 3 batteries together in reality so just + to+ & - to-, but fusing was mega important as it is in any wiring, one thing I always to without fail is to have a fuse next to each battery regardless if it is linking two batteries in the same place double failsafe, fuse sizing has always confused me, all I recall is fuse the cable not what it is powering in a 12/24v system.


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## wildebus (Jan 17, 2021)

Pudsey Bear said:


> I don't think I ever did a diagram nor Peter, it was just connecting 3 batteries together in reality so just + to+ & - to-, but fusing was mega important as it is in any wiring, one thing I always to without fail is to have a fuse next to each battery regardless if it is linking two batteries in the same place double failsafe, fuse sizing has always confused me, all I recall is fuse the cable not what it is powering in a 12/24v system.


I think the diagram was posted on Motorhomebuilder in fact and from memory was by Peter although not identified directly as such  (the description of the creator being a great help to many would certainly match the description of Peter).

Basically, the fuse rating MUST be lower than the ampacity of the cable, and it should be greater than the peak constant current draw of the circuit.
If you have multiple batteries in parallel, then the current from each battery will proportionally lower (so say you are drawing 600W via an Inverter from the battery - that would be 50A from the bank.  So if two batteries, 25A each;  if three batteries, 17A each, so you could fuse each individual battery on that basis.


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## Pudsey Bear (Jan 17, 2021)

Sir! That rates as the best explanation ive heard/seen.


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## Deleted member 76055 (Jan 17, 2021)

ChrisHunter.  Is your name Jose' because there is no way to do it like that.


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## Jack vdl (Jan 17, 2021)

Yes, that is a possibility, but I would say that unless there is a chance that the wires between the batteries would shortened to the metal mass, a single fuse between the batteries and the cable will suffice.
(By the way, being an electrical engineer, I think I know a little about this subject).


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## Pudsey Bear (Jan 17, 2021)

What sort of electrical engineer?

I would also use grommets when going through any metal, and a fuse at each end anyway they are so cheap..


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## trevskoda (Jan 17, 2021)

Pudsey Bear said:


> What sort of electrical engineer?
> 
> I would also use grommets when going through any metal, and a fuse at each end anyway they are so cheap..


I used a small length of corded hose when I took wires through a steel panel.


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## wildebus (Jan 17, 2021)

Jack vdl said:


> Yes, that is a possibility, but I would say that unless there is a chance that the wires between the batteries would shortened to the metal mass, a single fuse between the batteries and the cable will suffice.
> (By the way, being an electrical engineer, I think I know a little about this subject).


Qor you....
A single fuse between the batteries?
which side are you protecting?  the battery side or the battery side? 
And which side are you leaving unprotected?  the battery side or the battery side?


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## Jack vdl (Jan 17, 2021)

What I meant to say is that you can connect the batteries together without a fuse when there is no danger of the connecting wires coming in contact with the metal of the van.
For instance when the batteries are placed next to each other.
When this is not the case yo need to fuse the connecting wire at both ends next to the battery poles. And you have to fuse the cable that runs from the batteries of course also next to the battery pole.
The fuses are there to protect the cables against overheating or, in case of a short, getting so hot that they set the van on fire. If leading the cable trough a metal sheet/wall a grommet or other form of protection of the cable is a very good idea.
What kind of electrical engineer am I? A retired one and a general one. I have worked on installations in ships as well as in campervans.


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## Deleted member 76055 (Jan 18, 2021)




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## trevskoda (Jan 18, 2021)

lands43 said:


> View attachment 91410 View attachment 91410


Just a slight malfunction, some job cleaning the acid up, had you any cloths left after the job.


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## Turtletim (Jan 19, 2021)

I'm an electrician by trade and i see alot of amateur jobs that haven't come to harm by sheer luck. There's quite alot that can go wrong with a battery, even though 12v is not enough to drive current through skin, a battery is quite capable of releasing in excess of 500 amps if shorted, enough to send a spanner or the base of a van seat red hot in a very short space of time, let alone a thin piece of cable. All cables should be protected against overload and short circuit by at least one method, ideally 2. (IE insulation AND fuses /max demand calc etc) I'd size a cable according to ohms law and power equations, looking at how much it may reasonably draw in either fault or operational conditions to avoid overheating/melting. A 12v 2400w inverter can pull approx 200 (2400w/12v=200a)amps continuously so your looking at cables at least twice the thickness of those coming in your house to supply such equipment. So about 50mm2 between primary and supply, 35mm between 1st & 2nd battery if a 3 battery setup, and 25mm between 2&3 or on a 2 battery setup if all batterys are equal size and type. Welding cable is often pure copper so better that than jump leads which are often mixed with aluminium and can carry far less current for size. I believe regulations state the need for protection against vibration work hardening and subsequent failure of cables in vehicles, another reason to pick fine strand flexible copper cable over house type cable or aluminium. I'd size a fuse to not pop on max demand, and cables larger than that so they are protected. Personally, as well as sc/oc fuses in the positives as close as possible to the battery terrminals and on every cable size change/final circuit, i also place a fuse inline on the negative between the main and aux systems, that way if ever there's a bridge between chassis and aux live before the fuse (say in an accident or when tightening the live with a metal spanner) it'll disconnect it. Serves as an isolator between the van primary system and expensive secondary system equipment if having welding done etc also.
As battery cables are 2 way(charge and discharge) I'd also look at how much i want it to charge bearing in mind the the thinner the cable, the higher the resistance, the higher the volt drop between supply(alternator etc) and load/battery, and the less the percentage of charge the battery will finally obtain. A battery will require the full 14.4 v to charge to 100%, so you are looking at obtaining as  close to zero volt drop as possible in order to utilise the full capacity of the battery and maximise its life. Volt drop calcs can be found online and is far more of an issue in 12v systems than 240v systems.
I'd also mention hydrogen build up, its released when charging and is highly explosive so make sure you vent large or powerful lead acid battery systems. 
Hope this helps, I'd agree with the majority of posters here, the more i learn about electricity the more I realise how dangerous it can be and how much of an art it can be to get the most out of a battery system, so if in doubt consult an expert.


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## colinm (Jan 19, 2021)

Tookey said:


> Many could tend the bbq, drink beer and offer moral support as well, myself included


A seat for me to sit on to rest my dodgy hip, and I'm in.


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