Battery over charging? [Archive] - Forum


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06-21-2005, 04:05 PM

I just installed a new battery, alternator, tensioner and serpentine belt in my 99 GT. When the car is off, the battery reads around 12 volts. After starting the car, the battery reads 17.1 volts. I don't have any accessories on and I know 17 volts is too high, it should be around 14.5.

Does anyone have any idea what might be causing this or what I should double check?

Thanks in advance,


06-21-2005, 04:19 PM
bad voltage regulator.

06-21-2005, 10:07 PM
Thank you for your help. Is the voltage regulator inside the alternator or is it located somewhere else in the engine bay?

06-22-2005, 12:37 AM
Its in the alternator. Where are you getting this voltage reading? at the battery?

Also, did you replace the alternator with a Delco or aftermarket?

Those two questions are important. Just a spat of my personal beliefs here... there are three things that I won't buy from AZ, Advance, whichever part house: Alternators, Starters and A/C compressors. Sure they have a lifetime warranty.. but after you've changed your third alternator out within a year, you understand why the warranty is there.

06-22-2005, 06:29 AM
Bring the altenator back for a new one before you fry your brand new battery. Your right, the voltage should be about 14.5 volts, at 17 you run a higher risk of blowing every bulb in the car, more of a risk again if the voltage spikes above 17.

Even a rebuilt altenator should have a warranty.

06-22-2005, 07:19 AM
Thank you for all the help. I was taking the voltage reading at the battery. The alternator is a brand new Hitachi model with a five year warranty, not a rebuild. The guy at the parts store tested it before I bought it and he said it was good, but what do you expect for $7 an hour.

I'll take back the alternator and get another new one. The only brands they had were Champion and Hitachi. I'll get this done as soon as possible because I do not want to fry the brand new battery.

Thanks again for the help.

06-22-2005, 09:29 AM
you might not fry that battery but you could have some bad cells now, keep an eye on it even after you replace the alt to make sure it's holding the charge.

ie: check it first thing in the morning and make sure it's holding above 12 still