Car won't start

[330i Lover]

About 2 weeks ago my car wouldn't start. I couldn't even lock/unlock the car as the battery was so dead. I jumped it off my wife's car, drove it for about 5 minutes around the block. I tried it again in the morning and it was dead again. I jumped it again and took it to Advanced and they tested the battery, that's about 8 months old and said it's not bad but just needed to be charged. They charged the battery and after 45 minutes they said it was good. I drove home and drove it about 3-5 times without any issues.

I drove the car without any issues 3 days ago. This morning the battery is dead, once again. I jumped it off and drove about 45 minutes to work without any issues.

Every time I've had to jump the car off there hasn't been a light that's been left on, or anything that I can think of that could be pulling voltage from the car while it's parked. Any thoughts of what's causing the battery to drain so fast if Advanced just tested it and said it's not bad? I haven't made any recent changes to the car. Thanks in advance.

[san]

Did you check the battery voltage when the engine is on? I think the voltage should be a little above 13v when the car is running... I guess I would start there first to make sure the alternator is charging the battery like its supposed to...


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[330i Lover]

I haven't checked that yet. Once I get home I'll check the voltage while it's still turned on and report back.

[330i Lover]

The voltage was 14.2 while running when I got home. Yesterday and today it's started without any issues so far. I read that it pulls less juice to keep the car locked so unless it's being driven I'm keeping it locked to help pro-long the charge.

[san]

The voltage number seems to be what I would expect. But it seems hard to believe that the car would use so much more power if it's not locked...


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[ryankokesh]

14.2 is the right charging voltage. So your alternator is fine.

Just out of curiosity, how old is the battery? Do you have a sub, or other accessories?

[330i Lover]

Unfortunately today is another example of the car not starting. The last time I drove it was Monday morning both in the morning and in the early evening. I locked the car afterwards and it sat in the garage until this morning. I unlocked the car, turned the key and it started to turn but there wasn't enough juice to turn it over all the way for it to start up. I didn't check the voltage but I knew that I had a trickle charger from BMW and I needed to run errands so I put it on the trickle charger for about 2 hours, came back and it started right up without any hiccups. I drove it around on errands, never having issues with it starting and it's going to charge for the next day or 2 on the trickle charger until it's 100%.

I'm wondering if something is draining the battery while it's parked but no changes have been made and the checker at Advanced Auto says the battery, which was replaced earlier this year, has no issues. Grrrrrrrr!!!

[330i Lover]

14.2 is the right charging voltage. So your alternator is fine.

Just out of curiosity, how old is the battery? Do you have a sub, or other accessories?

No, I don't have a sub or amp. I do have the AVIN head unit that was installed last November. That is the only aftermarket electronic device in the car.

[alfakarl]

Out of curiosity has the car ever been in an accident? I have seen the main battery cable after an SRS detonation do this very same thing. All cables tight? If so I'd get a new battery and go from there. Failing batteries cause so many issues with these cars.

[TheFinanceGuy]

I wonder if something isn't shutting down? You could try pulling the amps being drawn once the car goes to sleep. Should be very little.

The 540 I had would do this. The battery would be fine for 2 days, but 3 days was too long. The factory nav computer wasn't shutting off - pulled the fuse for it, and all was back to normal.