I have a 2002 325i with 100k and it has a battery drain problem and it won't start sometimes (at least 3 times a week.) We have to jump it off. This started happening about 6 months ago and I got a new battery only to find that the other one wasn't bad. Took the alternator off and had it tested (it was pretty much brand new) alternator was fine. Sent it to an electric motor shop, they went through it and found nothing, said it was a new alternator. I came to the conclusion that the owner before had the same problem. I discovered something today, I knew something had to be running for the batt to drain like that so I put my ear up against the dash and heard a motor noise (no key in the ignition). I decided to pull the blower motor fuse, that was it , it went off. Now that I've found the drain what can I do to fix it ? has anyone had this problem?
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I suspect parasitic draw. All vehicles draw some power from the batteries when the car is shut off. Certain accessories such as clocks, radios remote door openers and alarms always need power. The normal power used is called parasitic draw.
It is always a very low draw so it doesn't run the battery down. If you install accessories like shortwave radios or plug things like inverters and portable refrigerators into the accessory socket and operate them too long without the engine running you can drain your batteries to the point where the engine won't start. If there is an electrical short in the vehicle or a malfunctioning accessory it could be drawing much more than its normal load causing a drain on the batteries. If you leave your door open and the inside lights stay on all night you could drain the battery down till the car won't start.
You would have checked the charging system before replacing the alternator, so I will assume the charging system is good. If the battery is being discharged overnight or over a few days, you would need to disconnect it and check every circuit on the truck to find the drain.
your battery is being drained ,, check the plug in for the towing light hook up , something is shorted across ,, clean and tighten all connections to the battery ,, once the vehicle is running,, check the posts with a meter, you should get a reading of 13.5-14.5 volts, if not your alternator isn't doing its job
"It won't do anything" means that there are no dash lights, no buzzers, nothing?
Any car has very slight electrical drains when it is shut off. For one thing, the clock is running, but there are a number of other tiny loads as well. With a good battery, you should be able to park a car for six months to a year and still start it.
However, if you start the car several times without running it long enough to recharge the battery, or if the drain is larger than it should be due to electrical problems or aftermarket accessories, you can get a failure to start.
Unfortunately, maintanence-free batteries don't tolerate being run completely dead very well, and many owners have unhappily found that draining an older battery once or twice was the last straw that ended their battery's life.
I suggest that you borrow a charger or a set of jumper cables to start the car, and drive it 30 minutes or so to fully charge the battery. If you have more problems, get the battery load tested at a shop that sells batteries to see if it is still OK.
Have the charging system load tested and make sure the alternator is charging.If this is good then you will have to check for a draw.If you have anything that is staying on and draining the battery or if you have something plugged into the accessory plug that could be draining the battery.You can check for a draw with a multimeter but this is a little more complicated if you are not familiar with this process.Hope this helps.Good luck.
Have you checked the alternator? The alternator may not be charging the battery. With engine running, check the voltage at the battery (it should be ~14V). If it's less than that, your battery won't charge properly. You can take your alternator to auto store to have it load tested also to be sure. Sometime alternator issues don't show up until it gets hot. Defective alternators have also been known to drain the battery after the car has stopped.