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also the battery i was using, the voltage was fine even with the negative terminal on...but once i turned the key to start it, the engine cranked twice and then the battery died..when i checked the voltage it was down to 9 volts; when i disconnected the negative terminal i let the battery sit for a while and an hour later when i checked the voltage the battery was back up to 12.3 volts, without even putting the charger on it...weird right?
Check the battery voltage before and after starting the car. The alternator should kick in and the voltage should increase to 13 or 14 something (if it is working).
You might want to check your charging voltage-or try different brands of batteries. Your battery is showing classic dead cell behavior, the plates inside one of the cells have shorted together and that cell no longer holds power. It might appear to hold a good charge but it's a "surface" charge, not a true charge.
12 volts is not really accurate-a fully charged lead acid cell will read a bit better than 2.2 volts, so 6 cells x 2.2 is 13.2. If you are killing batteries, you may be overcharging, long term undercharging, or possibly "deep cycling" the battery. Does the vehicle start easily or do you have to crank for long periods? Long cranking times heat up the battery internally, warping the plates, they touch, dead cell.
So-check for a voltage of 14.2 to 13.7 when the engine is running, if you have to crank excessively fix that issue, make sure the battery is mounted properly and not merely sitting in the tray unrestrained. And try a different store for batteries, although you may be getting new ones under warranty if they are only lasting a few months.
I have a 1998 isuzu rodeo and the battery in it is only 1 year old. i have ran parasitic draw tests and that is not the case here. the battery holds its charge no problem. the battery will read 12.6 volts with the negative terminal disconnected, when i reattatch the negative terminal the voltage coming out of the battery immediately drops to 10.2 volts; i read this is caused by a short somewhere in the wiring. how do i find this short? does anyone know?
--Thanks, Charlie
Shorted cell.
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