My teenage son drives a 2000 Ford Focus. About 4-6 months ago we purchased a new battery. 2-3 months later, while driving to school the car died and wouldn’t restart. About 30 minutes later we were able to start it and drive it to the auto parts store. They ran a diagnostic test on it and said the alternator was good but the battery was bad. Still under warranty they replaced it and it worked great for a couple months. Last night the car started but then died after driving it a couple of blocks and when we jumped it it started but then quickly died. When we try to start it it makes a clicking noise, but won’t turn over. I am wondering why our new batteries are dying. Anyone have any ideas? I am hoping to avoid a large mechanic’s bill… Thanks for any help!

After you turn the car off make sure everything goes off, had one car the brake light switch was malfunctioning, and the brake lights were staying on killing the battery, other stories, dome light, glove box light. sounds like a dead battery again, if you want to look in to it yourself here is a great link

+1 for Barkydog and make sure a qualified someone reads your alternator charging rate with a voltmeter just to make sure. A weak alternator can kill a battery in a few weeks.

Sounds like your alternator is bad, or possibly a bad contact or cable. I’d take it to a different place and get it checked. The battery may be bad at this point, as they do not handle a complete discharge without some damage.

edit:, as Mustangman states (following), it could be a high parasitic drain.

My teenage son drives...

Has your son installed a thumpin’ big speakers and power amp in the car for his tunes? It may be hooked directly to the battery instead of through the ignition switch and be draining it dry. Have a mechanic check to see if there is significant current being drawn from the battery when the car is turned off. It should be down in the 15-35 milliamp (0.015 to 0.035 amps) range.

Given the age of the car, someone should check the battery cables for corrosion. Make sure to check under the first few inches of the insulation, as unseen corrosion often happens there.

Agree! On a 15 year old car every electrical component is suspect. The Focus also had unreliable electronics, a good reason to check for “parasitic” power drains.

I agree with @Docnick

We have several Focuses in our fleet . . . and they’ve had a lot of interesting parasitic drains, caused by some interesting components

These come to mind . . .

ac head unit
instrument cluster

These were 3 different vehicles, by the way