0.2A drain resulting in battery going from 12V to 3V in 48hr

[g3org3y]

Couple of tests on the battery suggest there is a constant 0.2A drain. Unfortunately I can't locate the source (gone through all the fuses etc, perhaps the aftermarket alarm). It's not 'normal' but I don't think the drain is in anyway outrageous.

Couple of flat batteries in recent months (documented here) but it's getting silly. Left the car over the weekend, checked this morning, voltage was 3V!

Surely this suggests the battery has issues to discharge so much in that space of time, given the 0.2A drain.

When the battery is left disconnected, the charge is retained.

The battery is a Unipart item, via the AA with a three year warranty. Perhaps one of the flat situations has damaged something internally? I had a chat with a local auto electrician, he was of the opinion, given the drain and the timescale of the stationary period, there must be a battery fault.

Opinions much appreciated

[jimbobsimmonds]

What is the mAH rating on the battery...

Some fairly simple maths could solve this for you...

[JM]

g3org3y said:

When the battery is left disconnected, the charge is retained.

Doesn't sound like the battery is faulty then.

Are you sure the drain is 0.2A, how was this measured?

[andy-xr]

Boot light is a common one, not sure whether it'd be enough to pull the battery that quickly though

[g3org3y]

JM said:

Doesn't sound like the battery is faulty then.

Are you sure the drain is 0.2A, how was this measured?

Used an ammeter in series. Removed all the fuses and relays one by one, made no difference. Opening doors (thus causing interior light to come on) increased it. I believe it's an accurate value.

Something is surely afoot to go from 12v to 3v in 48 hrs.

[g3org3y]

andy-xr said:

Boot light is a common one, not sure whether it'd be enough to pull the battery that quickly though

Checked, and the glove box light, interior light, nothing under the bonnet. The alarm is my prime suspect.

Even with a 0.2A drain, I wouldn't expect it to flatten the battery to such an extent in such a short space of time.

This has only really been an issue since the harsh winter, prior to that, car was fine.

Battery is actually fairly new, 12-15 months old.

[E30M3SE]

Parasitic drain should be less than 0.05a, ideally around 0.03amps.

[g3org3y]

jimbobsimmonds said:

What is the mAH rating on the battery...

Some fairly simple maths could solve this for you...

The battery is rated at 64A/h which I'm assuming means it 'discharges' 1A for 64 hours. It will thus discharge 0.1A for 640 hours. With the ammerter measured drain of 0.2A, this would suggest with a fully charged new battery, it would take 320 hours to drain to totally flat?

I wouldn't be surprised if the drain has always been there but the cold weather (and lack of use) has affected the battery to the extent that it cannot sustain the drain.

My daily commute is typically a 60 mile round trip (all motorway) which perhaps would give sufficient charge via the alternator to otherwise offset the drain on a day to day basis.

[TheEnd]

If you get to 3v on a battery, it's dead.

[g3org3y]

TheEnd said:

If you get to 3v on a battery, it's dead.

That's my feeling.

Such a lovely day today, driving with the roof down (first time in ages) was a delight.

Finding it fairly gutting driving my sister's Ka (complete with teddy bear keyring) while the BMW is getting sorted.

[Le TVR]

Had exactly the same problem with a BMW318. Turned out to be the clock.

For some reason, sometimes when the battery was re-connected the current was around 200mA instead of 1mA. Never found out why.

[g3org3y]

Le TVR said:

Had exactly the same problem with a BMW318. Turned out to be the clock.

For some reason, sometimes when the battery was re-connected the current was around 200mA instead of 1mA. Never found out why.

Did you replace the clock/wiring?

The fact that the standstill period is reducing suggests the battery is slowly dying. Initially 4 weeks before it would go flat, then 2 weeks, recently down to 1 week and now 48 hours.

Will check it Weds am, if the battery is down to 3V I'll call the AA and explain the situation.

[LeeThr]

g3org3y said:

Le TVR said:

Had exactly the same problem with a BMW318. Turned out to be the clock.

For some reason, sometimes when the battery was re-connected the current was around 200mA instead of 1mA. Never found out why.

Did you replace the clock/wiring?

The fact that the standstill period is reducing suggests the battery is slowly dying. Initially 4 weeks before it would go flat, then 2 weeks, recently down to 1 week and now 48 hours.

Will check it Weds am, if the battery is down to 3V I'll call the AA and explain the situation.

Disconnect the clock and see if that makes any difference to the amp readings. But as has allready been said, battery really is not right. Get it tested.

[g3org3y]

AA guy came round today, explained the situation. Did various tests including drain levels - for 5 seconds the drain was 7A and then dropped down to what he considered acceptable/normal levels.

Boosted the battery (5.5V at rest) started the car. Then he ran a battery test which stated it rather nice bold capital letters: REPLACE BATTERY, which is what he did.

Genuinely nice guy, apparently he used to have an old E30 325i touring and latterly an old skool SAAB. Now rides Harleys. Good banter.

New battery now sitting in the car, the weather is sunny and I don't have any work today. I think I'll go for a drive with the roof down