# charging spare car battery with jump leads only.??



## dabnis (Jul 10, 2012)

hi guys...

i am new to this forum so i hope this is the right place for this question.

just wanted some advice on connecting a spare car battery to the crank battery on my tow car, with jump leads, to charge the spare as i am driving.

I am just doing this to charge the spare battery for the caravan as i have no hook up and cant afford a split relay for a couple of weeks.

the spare battery is in a battery box in the passenger footwell. I have fed the jump leads through the glove box to the crank battery.

I connect the positive wire and negative wire to the crank battery but i am not sure wether to connect the spare battery in the footwell BEFORE or AFTER i start the car.??

does this matter??

if i should connect them after i had started the car should i connect the positive or negative first??

my crank battery in the tow car is 45ah and the spare car battery is 60 ah does this make any difference?

someone told me about an isolater switch?  do i need one if im only topping up battery everyday on a 30 min drive?

any help would be much appreciated
thanks


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## n brown (Jul 10, 2012)

can't see why not,start car before connecting in case your dead battery affects the good one.connect the positive last.no switch needed as you just disconnect when charged.handy to have a bit of wood or plastic fixed nearby so as you take a clamp off you can clamp on the wood to keep it out the way


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## Sparks (Jul 10, 2012)

Post Deleted


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## ricc (Jul 10, 2012)

dont drive it with jump leads on the battery terminals... you only need one to slip and short out and you could be looking at fire and a total loss and youre insurance co will laugh at you.


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## Byronic (Jul 10, 2012)

Strictly speaking you should start the car without connecting leads then connect positive term. to positive term. first then neg. term. to neg. term. this eliminates chance of sparks ( battery gives off explosive gases). When disconnecting remove neg. first . then pos.
If you are driving, vibration may dislodge connectors such as crocodile clips. 
The difference in batt. Amperages is not likely to matter they are not vastly differing, but ideally should be same or as near as possible in power.


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## vwalan (Jul 10, 2012)

hi for years i used this system to charge a spare battery .i wired in one of those big red plastic key cut off switches . have it in the not connect position .start vehicle .once its running turn switch. just remember to turn it off when you stop etc . have fitted loads like it for mates . not keen on the relays i find they dont always work. and can catch you out. my way its just your fault if you forget.


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## dabnis (Jul 10, 2012)

*cheers guys*

nice one guys...

that was quick!!

i am going to remove the crocidile clips and attach to crank battery so theres no chance of slipping off.
change the crocidile clips for battery connecters on the other end so i can tighten for the spare battery in the footwell.
dont connect battery until after i have started the car. positive first and leave the window open.

all is good.
does that sound right to you??


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## Makzine (Jul 10, 2012)

I knew someone who disconnected a battery they had been charging and a spark ingited the gasses and blew the battery resulting in him being covered in acid.  I know its a very minor occurance and very unlikely but better to know than be covered in acid.  

Just my Personal opinion


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## vwalan (Jul 10, 2012)

i do know that things happen .we used to put spare old battery,s on the floor below a bench with a bench grinder on it .one day while grinding something a battery blew up. yes it can be messy. if its in a proper battery box it should be much safer.


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## Makzine (Jul 10, 2012)

vwalan said:


> i do know that things happen .we used to put spare old battery,s on the floor below a bench with a bench grinder on it .one day while grinding something a battery blew up. yes it can be messy. if its in a proper battery box it should be much safer.



I don't doubt that it will be perfectly safe as the OP is doing the right thing by asking first.  I just felt it worth my 2 penn'th


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## Byronic (Jul 10, 2012)

Oh no will this turn into a new gas attack  thread, ho ho. 

Wonder why Merc. and some other manufactures often make the drivers seat base the battery box (2 x 88ah in my case) seal the top with a gasket and put a little vent hole on the floor to vent out a lighter than air explosive gas, Hydrogen Sulphide?
Remember where minis used to house the battery... under the back seat, can't remember if that was vented though.


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## Makzine (Jul 10, 2012)

I'm not going to dissagree but was just relating an incident that I thought was relavant.            Which is why it was just a personal opinion.


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## Sparks (Jul 10, 2012)

Post Deleted


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## Byronic (Jul 10, 2012)

If you connect and disconnect in the correct sequence there is no risk in as much as there is no such thing as an absolute certainty.


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## Bigpeetee (Jul 10, 2012)

If the spare battery will fit in place of existing starter one do like I did, start engine to get warm, put partially flattened battery in start one and drive for couple of days, then before spare batt is flat, swap back, I did this for 18 months when I lived in caravan and never got stuck.


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## dabnis (Jul 10, 2012)

so just go for it then?

fixed connections, positive first, keep window open.


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## Byronic (Jul 10, 2012)

And don't forget an isolating switch itself may arc and spark and then....... BOOM. This is now definitely (defianltly?) a gas attack thread.


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## Teutone (Jul 10, 2012)

can't proove this with measurements but would hazard a guess that charging with proper battery terminals would result in less charging time compared to the croc clips where only some small spike will connect to the battery terminal?

Is a simple split charge relay that expensive? I could not be bothered to watch for the cables on/off all the time when starting the car. You can buy quick release battery terminals for less than a tenner QUICK RELEASE BATTERY CLAMPS TERMINALS QR | eBay
and relay is only £15 max Equip Split Charge Relay EQ320 | eBay


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## vwalan (Jul 10, 2012)

with a vw t25 the main battery is under the drivers seat .the spare battery fits under the passenger seats .i can say i have never known of an incident with that set up . i was only working with vw for years . also the batteries are normally close to the engine on many vehicles .think of the sparks going off in an engine bay with a petrol vehicle .could be at 4000rpm at least 16000.and thats only in the distributer cap.
you used to be able to get relays from lucas for about 6 quid . but turning a switch is much more reliable .


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## Canalsman (Jul 10, 2012)

Who had the vindaloo then ??? :lol-053:


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