Mysterious current leak

[300ZXNA]

My car went dead yesterday, and when I mean dead, I mean REALLY dead. The car wouldn't start with a jump, I had to put a charger on it for a few hours to get enough charge to start the car. The problem is that I haven't been able to find anything that was left on. Has anyone else had this sort of mysterious current leak? I really am not sure where to start searching on this one.

[andylv]

Check to make sure the connections from the battery to the car are not corroded. If you have volt meter check the voltage drop from the battery to the other end of the battery cables.
How old is the battery? After about 5 or 6 years batteries can die with no warning.
With the car running you should have around 14 volts across the battery. If the battery voltage is down around 12 volts your charging system isn't working.
If you don't have a volt meter go to an Autozone and ask them to check out you charging system. They can see how much of load you battery can handle and see if the charging system is working.
Only after verifying these items would I start looking for a current draws with the car off.
Do some searches on this forum and google for troubleshooting dead battery causes.
Good luck!

[drew1320]

I agree with AndyLV, have your battery load tested after it has been fully charged out of the vehicle, if it passed then start to focus on charging system, then to key off patristic draw.

If your not familiar with checking key off current draw use the google god to help you understand what your looking for.

[RRSperry]

1.) Get a new battery. Once you really kill an old battery, it's never going to recover...

2.) Fully charge said new battery BEFORE you put it in the car... It will last a lot longer.

3.) Buy a digital multimeter.. If you are going to do any work on, or even own an old German sports coupe, you better have some tools... Most DDM's will have a current setting what can measure up to about 10A. Connect the leads in line with the battery and check how many amps are being drawn. Anything more than about 300 mA is probably a problem. Start pulling fuses and see where the problem is.

You know... Pull the fuse, look at the meter, rinse and repeat.... until you find the circuit.

Quick and dirty... Check the trunk light. Does it actually go out? Check the trunk wiring loom on the drivers side of the trunk hinge, it's notorious for causing problems.

[fsmtnbiker]

Check all your interior lights. Often a door switch, trunk switch or glovebox switch will go bad and you'll have a slow draw that will completely kill the battery.

Also, always focus on *any* aftermarket electronics that are in a car first when it comes to electrical problems. I once saw an aftermarket stereo cause a truck's taillights to not work. Not kidding.

[LuxoM3]

The BMW batteries last about 6 to 7 years under normal use. If you can't remember the last time it was replaced it's probably old and dead.
This is a VERY common issue.

And no, when the battery dies, there is NO warning. You'll go to the store for milk. Turn off the car. Come back 10 min. later and it's DEAD.
Thus why I keep jumper cables in my car.

Once you need to jump the car, start shopping for a new battery.

[sak335]

While I agree with some of what has been suggested, I disagree with much of it as well. A battery is very unlikely to be permanantly damaged by a single discharge. However, a old battery will fall off a performance cliff quite quickly.

Best advice is to take it to a local parts store that does free testing and have both the battery and alternator tested. The battery drained for a reason and you need to determine that reason. Batteries are often blamed for electrical maladies and are not always the problem.

Report back once you have the tests done and we'll have a better idea of where to start looking (if necessary). And it's a good idea to start carrying either jumper cables (good) or a booster pack (better, if you have one) until you find the problem. BTDT.