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Dying battery

I have a 2005 Hyundai Accent with 60,000 miles on it. I have had it for about 3 years and it always worked great. It is my wife’s car and she only drives it 10 miles per week, and it has never been a problem. About 2 months ago it had a dead battery, one we purchased a year earlier. We took it back to the garage (not a dealer) who found it defective and replaced it. Our problem is that whenever it sits for 2 days or so the battery dies out completely, not even a click when trying to start it. In the last month we have tried 3 batteries (the garage does not charge for them) and just had the alternator replaced. Yesterday, after sitting for 2 days in Massachusetts cold, it was completely dead again, as dead as it can get. Does anyone have any idea as to what the cause could be. The garage cannot find anything draining the battery but it still dies totally. This was never a problem prior to 3 months ago. Thanks

The problem might be caused from a parasitic current draw on the battery as the vehicle sits idle. This can be caused by something as simple as a glove box/trunk light that remains on or it can be caused by a computer/module that fails to go to sleep.

One quick way to determine if there’s a parasitic current draw on the battery is to take an infra-red thermal gun and point it at the fuses. If a fuse is found to be hotter than the others, current is passing thru that fuse and that’s probably the circuit drawing the battery down.

Tester

It certainly seems that something is draining the battery. If you can’t hook up an ammeter to watch what’s going on, you could try pulling random fuses each time you park it until you find the one that cures the problem. That will get you pointed in the right direction.

It’s fairly simple for a skilled car-electrical expert to determine if something draining the battery when the car is parked and off. Likewise, checking theh alternator is just as simple. And testing the battery is simple with a load tester. Let’s assume the shop has done all this and there is in fact nothing draining the battery, the alternator is ok, and the battery is fully charged and ok.

In that case, you have to do some experiments. Does anything work at all when the battery is dead? Does the radio work? Does the stop-light work? Will the headlights come on? If all those things work, my guess is something is wrong in the starting circuit. Starting requires a very high current draw, as much as 100A. If you have even as much as 1/10 of an ohm anywhere in the starting circuit, that will give you a 10 volt drop and the car won’t start and may not even click. Even a 1/100 ohm resistance will result in a 1 volt drop, which could well cause the car not to start in cold weather.

So before proceding further, ask your shop if they’ve done all the above. If so, the next thing to check is the battery connections, the starter wiring, and the starter selenoid.

It’s amazing the shop keeps replacing perfectly good batteries without bothering to check for what the REAL problem is…If they can’t perform a “parasitic load test” they should not be in the auto-repair business…