Something draining my battery when car's off...

[94GTPilot]

So after I had the voltage spike, I took my alternator in to get bench tested. Turns out they couldn't do it (darn machine wasn't working) so since it was still under warranty, they just handed me a new one and "labeled" my old one dead.. Sweet!!

So I strapped the new one in, jumped the car and let it run for a bit to charge the battery. Let it sit over night and part of yesterday, and the battery went dead again. So I'm wondering, could something have blown, or be drawing power even with the car off?? kinda stuck on what it could be....

 

[Car Nut]

Could be a failing battery.

As long as you've made sure no interior lights are left on and of course, headlights, then you're in the clear. Even an aftermarket alarm takes only very very little juice (not noticeable at all).

I had this happen last week in my Jeep and a new battery fixed the problem.

On a stang, check/clean your grounds. There's no telling what all problems dirty grounds will cause, but my bet is on the battery unless it's newish.

 

[94GTPilot]

Yea, the battery is about 3 years old, so I would hope it's not the battery. The thing that started it all was a big voltage spike with my battery/ABS lights going on, then turning off after 5-10 seconds. Guess maybe I'll have to borrow a battery from a friend...

 

[HISSIN50]

WHen you go to swap batteries, first remove the negative battery cable. Put your DMM in series between the cable and battery post (set your meter to measure current draw in amps). Ensure all draws are off (lights are off, doors closed, etc). Then see what your meter reads. Seeing 50mA or so is good.

If you have a larger draw, start disconnecting fuses till the draw goes down. If that doesnt do it, pull the alternator cable off and see if that drops the draw (I know you have a new alt).

Good luck.