Help solve the Mystery of the Dying Battery!

[Diabolic 10+ year member]

Ok, this one has me at a loss for an explanation, and I seriously need help from anyone who might be able to identify the problem (and save me from wasting any more money!).

My car battery is dying. Sounds pretty normal so far, right? Except for the fact that I changed to a new battery and it kept happening, so I assumed it was my alternator. A test on the alternator showed it was working fine (~14.4V steady, 35A idle, 130A peak) but I eventually changed it anyway. New alternator, battery still dies.

Then I thought maybe my stereo was ******* the power while the car was off - although I checked to make sure all turn-on leads were wired correctly - and so I yanked the *entire* stereo, with the lone exception of the head unit. Battery still dies.

If I run the car for a while, it will charge and start again. If I leave the car sitting overnight, it dies. Completely dead, not just too low to turn the engine over.

Although the head unit is still in place, it has no power (that I know of) while the car is off. I unhooked all stereo-related wires from the battery - in case they were grounding or doing some weird thing that I hadn't thought of - battery still dies.

This all started about 6 weeks ago. The stereo had been in the car almost a year, with no changes and no dying battery.

I really need to know how to fix this. Any insight or help would be VERY appreciated! At least then, I could stop borrowing my girlfriend's car to go to work.

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[maylar 10+ year member]

First thing you need to get is an ammeter. If you have a DMM with a 10 amp scale, that'll do nicely. Then proceed like this...

If you have a capacitor in your audio system, remove it.

Verify that there is indeed current being drawn from the battery when everything is supposed to be 'off'. Do this by putting the ammeter in series with the battery positive terminal and the big red wire. By your description, I'd expect to see a half amp or more being drawn by something.

Start pulling fuses fom your fuse panel (and stereo wires) one at a time, while watching the ammeter. If you get lucky and one of the fuses makes the current go away, then you'll need to know what items are on that fuse, and track it down.

Don't be alarmed by small sparks when you insert the ammeter in circuit. There are capacitors in the radio and your car's computer that will spark when they charge. You're looking for steady-state current draw. You can ignore the measly couple of milliamps drawn by your clock.

Places to look are lights in the trunk or under the hood that could be on without you seeing them, or chaffed wires in your wiring harness.

Good luck.

 

[jbl_marshall21 10+ year member]

make sure ur battery terminal isn't screwed in really tight. mine was back in my old car and the end of the bolt punctured where the acid was at and leaked. just a possibility of happening

 

[John_Doe]

on some cars if your ground on your battery or your frame is bad, you will get a voltage drop.

 

[Matador 10+ year member]

i don't think it's teh stereo, u said u checked the remote wires n the grounds right?

it used to happen to me too, but the problem in my car was that the relays for the fans (master fan of the engine) were messed up so they kept runnin even after car is off.

i suggest you to do this:

once car is off, wait 20-30 mins, and check out your amp and see if the power led is on, then pop up the hood, and see if you can hear anything working. if there's try to isolate it and see which part it is n take it to the mechanic or see if u can fix that.

n i odn't tihnk it's the alternator if you siad that youhad it checked and it's fine. it's some electrical problem, something stays on all the time even when your car is off and that's why it drains the whole battery.

after you install a new one, how long does it take to die?