CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

What' swrong with this old car?

My daughter has a 94 Chevy Lumina. Her car stop working a few days ago. I jumped the car and let it run for about ten minutes to charge the battery and it worked fine. Later that evning I went out to start it again and it wouldn;t start so I figured it just needed a new battery. I purchased a new battery and it started up right away. I did not drive the car after installing the new battery. The next morning when I tried to start the car the battery was completely dead. I know it’s not the alterator because I never drove the car after installing the new battery the night before. What could draw a new battery down completely by letting it set over night without even driving the car? Could it be some type of electrical problem. I’m stumped!!

Get the engine started, and with a voltmeter measure the voltage at the battery connections. It should read 13.5-14.5 volts DC. If it reads 12.5 volts DC and drops, the alternator isn’t charging the battery.

Tester

There is some kind of parasitic load on the electrical system. Finding it will be the hard part.

For starters (no pun intended), I would suggest that you disconnect the trunk light and the underhood light (if so equipped), since the switches on these devices can malfunction and allow the lights to be on at all times. If the car has a security system, that is another possible source of a parasitic load on the electrical system.

If neither of these suggestions turn out to be the source of the parasitic electrical load, the remaining possibilities are really numerous. You may need an automotive electrical specialist.

Thamks. I don’t think it could be the alternator because after I installed the new battery I never drove the car.

If you run the engine for ten minutes, and the alternator isn’t charging the battery, the engine is running off the battery. Which is going to run the battery down. If the alternator has failed because of short, this can prevent the battery from recovering from being drawn down.

Never assume anything. The next step is to check the alternator output.

Tester