Flat battery, cause? Can you check with OBC options?

[Scarab 330ci]

Last used the car on Saturday and started on the button as normal, came back from the shops, parked up and undone the windows a little as it was a hot day. Started raining later in the day so went back and done windows up, didn't use it again till this morning and was totally dead, not even enough juice to power the central looking or interior lights. Got a jump start and started fine took it on a 20 mile run this morning and again haven't used it since. Is there a way using the OBC options you can test the battery?

My old e38 had a draining battery so I sure as hell don't want the same in this.

Any ideas what could have drained the battery so much?

[Rich_D]

You can't test the battery using the OBC menu, you can only read the voltage

If the battery is old, it's probably just starting to fail, they can go quite suddenly from personal experience.

However if it's a drain then I'd be looking at the final stage resistor

[Scarab 330ci]

You can't test the battery using the OBC menu, you can only read the voltage

If the battery is old, it's probably just starting to fail, they can go quite suddenly from personal experience.

However if it's a drain then I'd be looking at the final stage resistor

It may well be the original battery, just tested the voltage and it said "122 9" on the dash?

Seemed to unlock fine etc but didn't want to start it as may be a few days till I use it again.

Any other way to test the battery?

[Rich_D]

Reading the voltage won't tell you much, you can have them load tested, places like Halfords do it FOC

[2000E46CONVERTIBLE323CI]

A few years back, I had some trouble with the original battery in my vehicle.

Wasn't driving the vehicle much at the time which probably made things worse.

Bought a replacement from BMW's for around £150, which only lasted

a few months before that started playing up. Took the battery back to BMW who

gave me some nonsense about not exchanging or refunding it unless the battery

was on the vehicle so they could run some tests and if they found that something

on the vehicle was causing the drain, I'd be lumped with the costs of their tests etc.

In the end, decided to stop wasting my time and energy at BMW's and get myself a real battery instead.

Went for a Bosch and haven't had any problems since.

The Bosch was roughly half the price of the battery from the stealership, although I did pay around £100

for it since my mechanic sourced and fitted it - he obviously added a little cut for himself.

For anyone in need of a new battery for their E46, I strongly recommend you go for a Bosch.

Do not waste your money on crappy, problematic, batteries from BMW.

[JayP07]

Recently solved a battery drain problem... long story short it turned out to be a combination of a faulty FSR as Rich mentioned and a faulty cd player in the boot that kept flicking through the cd cassette when the car was off. I removed the cd player and changed the FSR - no more dead battery. Before i figured it out I bought a new battery to be on the safe side but it still happened until i found the cause. I used a multi meter to test the battery draw.

Edited August 6, 2013 by JayP07

[Scarab 330ci]

Used the this morning, 2 days after the jump start, and started on the button, not sure what caused it to drain, maybe it will do it again but fingers crossed it ws a one off.

[bobdisk]

My battery always went flat after about 10 days if I didn't use it, holidays and the like. I use it almost every day, so no probs then. Turns out to be the engine cooling fan taking a little bit, not enough to turn it. Only found it out this week, and have had it for some years I am in the process of trying to sort the fan control without having to buy a whole new fan for a lota money.

Edited August 19, 2013 by bobdisk

[JayP07]

My battery always went flat after about 10 days if I didn't use it, holidays and the like. I use it almost every day, so no probs then. Turns out to be the engine cooling fan taking a little bit, not enough to turn it. Only found it out this week, and have had it for some years I am in the process of trying to sort the fan control without having to buy a whole new fan for a lota money.

Are you certain this is not just the FSR turning the fan on while the car is off which is what was happening to me?

[bobdisk]

Are you certain this is not just the FSR turning the fan on while the car is off which is what was happening to me?

Quite certain, I thought it might be that, so I disconnected the FSR last time I went on holiday, same results. I found it was the engine fan by putting an ammeter in series with the battery, letting it go to sleep, and pulling all the fuses one by one. With the 50A fan fuse out, sleep current dropped to 40 mA. Next time I leave it, I will pull the fans plug and see what happens. I would like to get hold of a fan controller, and see whats inside.

[JayP07]

Are you certain this is not just the FSR turning the fan on while the car is off which is what was happening to me?

Quite certain, I thought it might be that, so I disconnected the FSR last time I went on holiday, same results. I found it was the engine fan by putting an ammeter in series with the battery, letting it go to sleep, and pulling all the fuses one by one. With the 50A fan fuse out, sleep current dropped to 40 mA. Next time I leave it, I will pull the fans plug and see what happens. I would like to get hold of a fan controller, and see whats inside.

Fair enough... good thing you took the time to eliminate the FSR...post the results when you get round to it mate, good luck with that.