[Shotimes] Battery/Alternator/Voltage question

[Steve Tatro]

What's up.

Got a stupid question, actually more than one.  What kind of VDC should
I get from my battery, with the car off?  I measured it after driving
around and it was 12.6V.  Also, what should the voltage be with the car
running?  I measured 13.5V.  Also, again, what voltage should I expect
when I go out to my car today after it's sat out in the cold for 10
hours?

What I'm trying to figure out here is if there's a simple way to
diagnose if the battery is good or going bad, and the same regarding the
alternator.  I'm assuming if it sits all day the voltage will drop, and
if it drops too much then my battery may not be holding a charge
properly.  Also, if the voltage measured is too low with the car
running, do I possibly need an alternator rebuild?

Anyone?

Thanks as usual.

Steve Tatro
Red/Black '93 with 164k miles
Cincinnati, Ohio
www.picturetrail.com/stevetatro