# Battery Testing



## T J (Mar 4, 2010)

Low funds dictate I'm gonna get a second hand battery from the breakers to get me going.
( Not wanting to restart the leisure/starter battery debate)

Any advice on battery testing would be great, total dope with electrics atm, just bought my first multimeter 

I want to test the battery on the van too, I may give it a new one and use the old one as the second one.

Thx
TJ


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## Pioneer (Mar 4, 2010)

Hi T J,
take your batteries to your local garage and have them tested under load.
Charge them fully first, they will tell you if they are worth keeping or not.

Happy Camping


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## PaulC (Mar 4, 2010)

From what I've seen, a tool with two prongs are connected to the terminals, to draw a load. If the voltage falls below a certain value. if it's fully charged, it's duff. Just to use a multimeter will not do the job as it has to be tested under load conditions.


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## Deleted member 775 (Mar 4, 2010)

normaly a breakers yard will either have tested the batts or else they will do a test there and then ,but you can also chech the batt date of manurefacture if it is a newish one then it aught to ge ok . i personaly have always gone to a breakers yard for batteries also replacement parts including tyres you can get some bargains if you know what you are looking for .


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## Hallii (Mar 4, 2010)

The "voltage drop" test is a crude but effective method of destroying a perfectly good battery! The current drawn can cause the plates to heat and buckle, result - one dead battery. Note that the same dropper is used for the smallest to the largest battery, the large "heavy duty" batteries might take it, but not the very small petrol car batteries.

Best test is to charge it for 24 hours and to check the Specific gravity of each cell a few times during the day, if one cell is defective it will quickly show up as a very different reading.

The problem with this is that if a SG reading started off at 1.285 when fully charged and brand new, After 12 months use the battery could be fully charged for say 24 hours (or until the charge current has fallen to a very low level) which effectively means the battery is as fully charged as it can ever be, yet the SG reading will be substantially lower, say 1.265. If this SG reading is compared to the data sheet for the battery then this might show the battery to be at 80% charge state. It is at 80% charge state. But it is at 80% charge state of the charge state of a brand new battery. It is not at 80% charge state for that particular battery. It is at 100% charge state for that particular battery. 

So best bet is to buy a second hand one and agree that if it's a "duff" one that they will swap it. They have always agreed this with me, not for batteries but for other second hand parts.

Hallii


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## NicknClair (Mar 5, 2010)

As per Hallii's quote, it is a def no no to "drop" test a leisure battery.
A quick way is if you use your multimeter and monitor the leisure batteries (once fully charged) before and after a 24 hour cycle, the voltage should never drop below 12.7 volts (this is based on the leisure battery being disconnected whilst you are testing, therefore minimising any influence on the leisure battery). If you find this has dropped below this typical figure, then it is a sure sign that it is on it's way out.
The best way is to find a local *battery* specialist (not a garage/Halfords etc etc), which will have an advanced tester without running risk of damaging the batteries (we have invested in such a product, est cost was I think £300/£400). He will probably charge you say £30.00 for the service, but you will get a definitive answer without risking damage to the batteries.
Happy Hunting!!!


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## PaulC (Mar 5, 2010)

Hallii said:


> The "voltage drop" test is a crude but effective method of destroying a perfectly good battery!



As I understand it the load is not a short circuit but equal to providing a starter motor load! So therefore should not present a problem to a battery.


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## NicknClair (Mar 5, 2010)

PaulC said:


> As I understand it the load is not a short circuit but equal to providing a starter motor load! So therefore should not present a problem to a battery.



This is true in a sense, but leisure batteries are different in their construction/desgin, i.e the plates are long and thin that can easily buckle under load, whereas an engine battery is designed for heavy load, but doesn't carry the A/H capacity of a leisure battery. Engine batteries are based on CCA's (cold cranking amps) and leisure batteries normally do not carry and figures relating to this. The tester we use asks for the values when testing to determine the correct way to test the battery connected to it (including battery type, gel/lead acid). hence the reasons for suggesting to go to a specialist.


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## PaulC (Mar 5, 2010)

nickjvanbitz said:


> but leisure batteries are different in their construction


Yes true "leisure batteries" which are deep cycle batteries, are of different construct. However what is on the market are only re-badged starter batteries as a true deep cycle battery will cost about £700. The manufactures are pulling the wool over the public's eyes to make a fast buck!


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## PaulC (Mar 5, 2010)

basildog said:


> not too upset with that if it lasts !!!!



Well if you have a correct charge/discharge cycle no doubt it will!


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## T J (Mar 5, 2010)

Thanks for the replies 

hot topic batteries  

spoke to the local breaker who said he has small batteries at £10 and large at £15,
will pop down tomorrow and check them out, I'm after a tray too.


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## mildred (Mar 6, 2010)

*Battery Voltages*

I've posted this table before - but as it's a perennial issue here goes again:

State of Charge - Whole 12V battery Voltage - Volts per Cell

100% - 12.7 - 2.12
90% - 12.50 - 2.08
80% - 12.42 - 2.07
70% - 12.32 - 2.05
60% - 12.20 - 2.03
50% - 12.06 - 2.01
40% - 11.90 - 1.98
30% - 11.75 - 1.96
20% - 11.58 - 1.93
10% - 11.31 - 1.89
00% - 10.50 - 1.75

These are the voltages that are to be expected having "fully charged" the battery and then removed the "surface charge" either by putting a load such as the headlamps on for 5 minutes or letting it stand overnight.

I include the Volts per Cell value for completeness - but if you don't know what you're doing - *DON'T* attempt to test individual cells.

It is suggested (both in this forum and elsewhere in special interest groups) that if one is using a lead-acid battery in a leisure role that you should never,ever, not-at-all, go below the 40% level before recharging if you want to have longevity and effectiveness from your chosen battery.

MildRed


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