so i got my batt checked, it was good. i got my alt tested, its good.

today i checked the batt voltage with the car off it was 12.48, which is normal. when i turned on the car, the bat was visibly getting drained, i could watch the batt guage just slowly drop until the car was souly running off the alt and it was idling at 1100, getting higher as the car was left on longer. the car was only on for at the most 7-8 minutes until the batt was drained. when i shut off the car i did another voltage test on the bat it was a little lower than 12.38? i dont get it, when i turn the ignition key half way the batt guage wont even go up that high it stays just over 8 volts, not enought to even crank the motor.

i have no clue as to what is causing my car to act up like this, oh ya it seems to do this on the nice days outside too which really pisses me off. someone please help me, what could be draining the batt in less than 8 minutes right after the car is turned on?

 

oh one other thing, when the car is left alone for a while the battery voltage seems to go back to normal but when i turn the key it goes back down and cant even start the engine.

 

Sounds similar to when I used to short circuit things in physics lab sophomore year in college

Take your battery and alt and get them tested elsewhere. I've found that some places aren't reliable, and sometimes they'll test good when they aren't.

You should test the battery and alternator voltage with the car running. Each should be around 14 volts, if not, something is wrong with the alternator or the wiring.

You say the battery was drained after 7-8 minutes, but read at 12.38 volts of potential between terminals? That makes no sense.

 

ill try to get them tested elsewhere but like you said, it makes no sense as to why the batt read normal after the car died.

another thing i forgot to mention is that before when the car was running the batt voltage would be 2-3 volts lower (9-10.47) than when the car was off (12.47). something sucks out the voltage when the car is on, but on some days it would just suck to 10.47 and not get any lower or drain, and on nice days i would start the car and it would just drain the battery.

 

First, you can't go off the voltmeter in the car... so you need to use a Digital Volt Ohm Meter DVOM, and test the battery terminal to terminal to get the right voltage.

If your battery voltage is the same/good all the time it is your alternator.

Different shops test alternators differently. Some hook up to a machine and test the leads, some (like napa) set it up to run VIA Belt like it was actually on the car. I've had an Alt good and bad at different places.... it was bad. If you get a bad reading from anyone. Most likely, it's bad. But you need a couple of "good" tests to really confirm it's good.

Find a good parts guy that's willing to help you also, some are just lame and say oh it's bad.... after taking it to the back and getting a soda instead of testing it.

 

im just gonna throw this out there, but could i have bad wires from the alt to batt? because when off the batt reads normal (with a batt tester) and when the car is one it drops like 2 volts? its as if the alt drains the batt but that wouldnt explain this 7 minute draining that doesnt happen all the time.