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Dead battery or something more sinister?

Hello all,

I recently had a new battery put in by Pep Boys. The old one was 3 years old or so and after leaving a lamp light on one or two times and getting it jumped, it started to just not turn on if I didn’t drive it for a couple days or so. So we had Pep Boys put a new one in and thought that solved our problems. Went and got some muffler work done and thought we were good to go for a while. It now has around 160 thousand miles on it.

Went on vacation from April 10th to April 17th, and when I came back it wouldn’t start again. Completely dead when I turned the key. No lights, no nothing.

Got it jumped once more and drove it straight to a mechanic we go to a lot and he kept it overnight and said he ran all the tests he could and he concluded that the battery is bad. He said that the voltage should read 9.7 but it was reading 9.4 after sitting for a night. Alternator and everything was checked and everything looked good.

So I took it back to Pep Boys today and they said they tested the alternator and amperage and everything was beautiful.

I’m pretty dumfounded. I told Pep Boys to keep it overnight and see what the readings are in the morning/early afternoon tomorrow.

Also, let me be clear: I am not continually leaving the lamp light on. :slight_smile: I’ve double triple checked that.

Anyone have any ideas?

Thanks for your time.

I think you need to find a tech that knows what to look for.

There must be a bad ground connection, a parasitic drain or perhaps the alternator is over charging and killing the battery.

Fully charged battteries should read 12.6V not 9.?.

Somebody’s goofin’ off here.


This is what I meant by the voltage thing.

Bear in mind I know next to nothing about cars, and this is the info my dad gave, which he got from our mechanic who is not Pep Boys.

There is obviously something draining that battery, but what? That is the question.

You need to take the vehicle to someone who can test for a parasitic current draw on todays vehicles.

In the past all one had to do was disconnect the negative battery cable and connect a test light or meter between the battery post and the end of the cable. Then if the light came on or the meter showed voltage there was a current draw. Then you would pull fuses or relays until the light went out and that would tell you what circuit to check for the current draw. But this can’t be done on todays vehicle.

Todays vehicles have computers and modules that control various circuits in the vehicle. And these computers and moduls can remain AWAKE for up to an hour after the vehicle is turned off. Afterwhich these computers and modules should go to SLEEP. If one of these computers or modules fail to go to sleep after the vehicle is turned off it can draw the battery down as the vehicle sits. If this happening, and the negative battery cable is disconnected it forces all the computers and modules to go to sleep. So when you go check for the parasitic current draw it’s not there.

The only way to test for a parasitic current draw on todays vehicles is leave the battery connected. And then test for a voltage drop across the fuses for each circuit.


Thanks, Tester. I guess that is my next step. I asked the guy at Pep Boys what it could be if it wasn’t a bad battery and he told me something to the effect of what you just posted.