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LJ71 Battery rating, what should i have?

JimmyLJ71

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Joined
Jan 30, 2011
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186
Just got my truck back from the engine man, one of the batteries is shot, don't know which one yet.

I would have thought they should be the same rating but i have one 100amp and one 70amp, what should they be?
 
Same rating (matched) batteries is right :thumbup: I am sure that a matched pair of either size will be more than adequate. If you can fit 100Ah (or bigger) batteries in, then go for it as the extra current may come in handy some day :mrgreen:
 
Charged the batteries up overnight, they charged ok, put my multi-meter on them, there both currently reading 13.5 volts, going to give it 24hrs and try again.

When you take them to be checked at the garage don't they check the amps?, they use those big clamps with a meter in the middle don't they?
 
Batteries are tested using a drop/load tester.

A Drop/Load tester- creates a load on a battery, you read the voltage before, during and after. If you have fully charged battery meaning on a (12volt battery) you have 12 volts or better, you load the battery at half of the rated cranking amps for 15 seconds, the volts should not drop below 9.6 volts during the test and the volts should recover within 15 seconds to above 12 volts after the load has been removed. If it doesnt then check the levels and specific gravity of the acid in the cells and if all is correct and it still fails the drop test then it generally means one or more of the plates in the battery cells has warped or corroded and the battery is dud.

As above you should ideally have a matching pair of batteries of the same make, ratings and age otherwise you will generally find one battery tries to discharge the other.
 
Not something i can do then :thumbdown:

I will have to find someone to test it for me.
 
JimmyLJ71 said:
Not something i can do then :thumbdown:

I will have to find someone to test it for me.

Hi Jimmy

A few more things to consider:

Are the batteries connected in parallel ? if so then you should have batteries of the same rating , if one is connected via a split relay it is not as important !

There are places that will check your batteries (like Halfords (I think) or a dedicated battery supplier) but watch as they might just want to sell a battery.

The last and I think the most important thing if you do have a duff battery then change both (only if in parallel ) as the new battery will pull down the other battery, so both need changing !
 
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Don't know if connected in parallel or not :oops: , if Roger is on line he would know, it's connected as standard on the LJ71
 
Yup they will be in parallel. Any decent motor factors or auto electrical specialist should be able to do a drop test for you and its usually free. I wouldnt trust the Halfords monkeys to fit a valve cap to my vehicle! Also make sure you disconnect the batteries from each other before they are drop tested otherwise youll end up testing the good one and it will skew the results.

FYI batteries are expensive at the minute due to the increasing price of the metals used. So its doubly expensive as you have to replace both even if only one is duff. :doh:
 
Turns out my mate had a tester, he fits fire alarms, amazing bit of kit not one of these big clumsy things, an electronic gadget that you connect up and by taking a reading and looking at a chart it tells you if the battery is ok.

Anyway they are both knackered :(

Looks like the older larger one has started to fail and has taken the smaller newer one down.

Now i have replaced them both it all works ok. :thumbup:

Just a bit more advice if i could. :D

I use my truck for overland holidays so i have a few accessories like a fridge etc connected up via a new fuse box, at the moment i have that connected to the battery nearest the bulkhead, would this be the correct way?, would this bring one of the batteries down?
 
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