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Old 2008-07-29, 10:57 PM   #11
sperry
The Doink
 
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Real Name: Scott
Join Date: Nov 2002
Location: Portland, OR
Posts: 20,335
 
Car: '09 OBXT, '02 WRX, '96 Miata
Class: PDX/TT-6
 
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Quote:
Originally Posted by Dean View Post
I agree, those voltages sound low. You could have a shorted cell and/or a bad regulator. A 1/2 decent battery with a full charge should be able to hold over 12.5 volts with a >50 watt headlight across it for at least a minute. A good one for probably 30-60 minutes.

Even float charging on a good battery happens at about 12.5-13 volts and 14-15+ under heavy charging after starting or other heavy discharge.

The fact that the system will go above 13 volts means it is likely not the alternator IMHO.
The fact that I'm on my fourth optima battery in like three years tells me something is wrong with the charging system. I think the alternator works, just not well. I figured there was something draining the battery while it was off, but I checked that and I'm barely drawing any current for the clock and remote start receiver.

So it comes back to the alternator, which never gave me a problem until my radiator sprung a leak and I was forced to drive for an hour spraying coolant onto it. That made the regulator go out and I replaced it with the Napa part. Ever since then I've been eating red tops. I belief you've got several or them at your house right now. Are they bad?
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