Battery Discharging problems.

[88WhiteGTConv]

* UPDATE* Battery Discharging problems.

Im just wondering what are the possible causes for a battery to lose voltage. I have tried everything to find a short but i cannot. It seems to do it wether the bat is plugged in or not.

Can a bad battery discharge on its own? It goes dead in about 24-48 hours of sitting. My car sat for about a month and then i went to turn it on and it was dead, i jumped it. Ran it for about 10 minutes shut it off....came back about 2-3 days later and it was dead again. I charged it for 10 minutes again, then it sat for another 2 days and bam....dead again.

The bolt meter was showing around 7-8 volts out of the bat. When the car is on im running around 14.2 volts. When i turn the car off after 10 mintues the bat reads right around 12.0 volts but starts disapating immediatley....i cannot seem to find the cause.

What do you guys think?

How do i try and figure this one out.

Mike

 

[865.0HO]

Hook up a battery charger and put it on a 2amp charge overnight and see if your situation improves.

Disconnect the positive battery cable and watch for any small sparks when the cable is touched to the battery.

 

[jrichker]

Typically it is something draining the battery. Small things like glove box or courtesy lights are often the culprits. If you have an aftermarket stereo or alarm system, it is also suspect.

The ideal method is to disconnect the positive terminal, and connect a Digital Multimeter (DVM) between the positive terminal on the battery and the positive cable. Set the DVM on a low current scale of 2-5 amps if it doesn't auto range. Watch the current draw, and then start pulling out fuses. When you see a sudden drop in the current, that circuit is the likely culprit. Note that the computer, radio & clock will draw less than 1/10 amp to keep the settings alive.

 

[Kiknads]

when my alternator went bad it was sucking juice when the car wasnt on

 

[88WhiteGTConv]

Well here is the update


I did what you said and disconected the terminal on the positive side and was reading from the post to the terminal...catch is i couldnt read amps...so i was reading dc volts.

My buddy was watchin the meter and i went to hop in the car....as soon as i opened my door the volts jumped from 12.2 to 13.1....were like wtf......anyways....when the light is in the off position with the door closed the voltage drops...if you turn the light on, or open the door so the light comes on the volts jump back up....kinda wierd so i just disconected the harness to the rear view mirror....think that was the problem..


What do you think?

Mike

 

[HISSIN50]

Well here is the update


I did what you said and disconected the terminal on the positive side and was reading from the post to the terminal...catch is i couldnt read amps...so i was reading dc volts.

My buddy was watchin the meter and i went to hop in the car....as soon as i opened my door the volts jumped from 12.2 to 13.1....were like wtf......anyways....when the light is in the off position with the door closed the voltage drops...if you turn the light on, or open the door so the light comes on the volts jump back up....kinda wierd so i just disconected the harness to the rear view mirror....think that was the problem..


What do you think?

Mike

im certainly no JR, but here is my take. when you do JR's test, the assumption is that you have nothing at all on. i would have pulled the interior light fuse first thing. you would have to get in and close the door (or push the door pin switch). then do the tests. once you can rule that circuit out, leave the fuse out so you dont have that draw.

the test is lookin for relative draw. so when you pull a fuse with a short, the voltmeter reading will change. as you saw, the test works (ive never done it with the volt setting though).

so try the door test again. then try all the fuses. obviously, check all the wiring you can for shorts. sometimes alt cables will chafe and burn (not on stangs, but other cars). same idea though.

if this really bothers you, you can get a short finder. it is a magnetic deal and a probe (or something like that). Jerry says he used his and it worked (i have one but have not cracked it open).
my ramblings.
good luck.