A friend of mine has now had several instances where his battery has gone dead in his "non-Ford truck" (ok, it's a '95 GMC Yukon, there I said it!). This has now happened about 3-4 times over the past couple of months. All the times it has happened, he's found it dead when he goes to start it for the first time that day, and I think all the times are after the car has sat for at least 1 day. The battery is around 1 year old (DieHard Gold). Each time it has happened, I've brought over my charger and although the battery is always completely drained, I've managed to recharge it, and it always seems to work for him for a few weeks. Unfortunately it just seems to happen at random, and we can't identify any particular activity that causes it.

This most recent time I decided to do a little test. I recharged the battery for a few hours, and then disconnected the battery from the car. I checked the voltage the following day and it showed 12.18. I thought that was a bit low and initially suspected an internal short in the battery, but decided that since it was still taking a fair charge when I pulled the charger the day before, maybe that was still an ok voltage. I rechecked it 24 hours later, and got the exact same 12.18 volts. That lead me to believe the battery is not internally shorted, and that the problem must be in the car. I did notice a bit of corrosion on the side terminals as I pulled the cables, but nothing major (and I'll clean them up before reconnecting them). The one other thing I did was connect my meter in line with one of the cables, and measure the amps that the car was drawing with everything shut off. Initially I was getting just shy of 1 amp, but after about 4 seconds, that dropped right down to I think about 0.1 to 0.2 amps or so. That seemed ok to me.

This has happened too many times now to just be a coincidence (like a door being left open). Each time we recharge the battery, there are no lights or anything on when the power comes back up.

I'm willing to try some troubleshooting, but I'm looking for some tips on how to approach this. I know AutoZone will do a charging system check for free - maybe that's a good start. I'm wondering if something like a bad diode in the alternator would do this? Obviously a loose/frayed wire could cause an intermittent short, and could be anywhere on the vehicle. Any advice for me? Thanks!

 

If there was a problem with the charging system, he should get an indication on the dash somewhere(light should flash or something). He would also notice the lights going dim or something if it was not charging, especially at night with the wipers and such on too. It sounds like you have a drain on the system, and it sounds intermittent. So it's not going to be easy to find. Anything added aftermarket would be a suspect in my book, like stereos and TV/dvd players, etc.