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Battery Drain.

Pete Attryde

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My truck is not getting used much at the moment and has sat for a fortnight unused on a couple of occasions recently, both times the battery has been too discharged to start the engine (it would turn over but not fast enough to start it.)

I spent this weekend with the multimeter and discovered that with every thing switched off, doors closed etc, there was a total drain on the battery of 80mA. this seemed a bit high to me but I am not sure if it would be enough to discharge the battery of this time period. The battery is brand new by the way so should :ph34r: be good. Truck is a 1996 300 TDi Auto.

I have already found that due to the way the stereo was wired this was causing 60mA of the drain and I have sorted that, I just want to know if I could be looking at a duff battery as well as a highish current drain.

The battery takes a charge no problem and once re-charged starts the engine with no problem.


editted for spelling.

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So, does that mean your drain is now only 20mA ?? Or was the original drain 140mA

If it's now 20mA, that's fine. If it's 80mA, then somethings still draining.

Is the surface of the battery clean? I've seen parasitic drains caused by dirty/damp battery tops shorting between the terminals. :blink:

Average levels of current draw:

Voltage regulator. 1-2mA

Clock.................. 3-4mA

Radio.................. 5-7mA

ECU.................... 6-8mA

It's easy enough to get the battery checked, nip to kwik-fit/halfrauds or the like and ask them to test it. Point out it's still under warranty, so you won't be buying one from them, but you want to check it before going back to the place of purchase, so you don't make a fool of yourself. ;)

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Technically probably not enough:

80ma = 0.08 amps

14 days x 24 hours = 336h

0.08 x 336 = 26.88Ah

which should only be about 1/3 to 1/4 of the actual capacity depending on battery size (the one in a Td5 Discovery is 110Ah for instance)

However in practice it probably will kill it in that sort of timescale, certainly not much longer, and also bear in mind that the drain was there when you were using it too so it is unlikely the battery was fully charged - alternators do not make a good job of bringing batteries right up to full charge when they are well down like that.

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yeah the drain is now down to 20mA which i am much happier about.


Cheers for that, I had thought it might be enough just wasn't sure.

I think I may well invest in an optimate type charger to keep the battery topped up when I'm not using the truck.


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