It is charging? Should be between 14.3v and 15.5v on a brown running at a
fast idle, minimal electrical load, after having had enough running time to
put the cranking energy back into the battery. Turning on electrical stuff
like headlights and brake lights will drop the voltage significantly, but
I'd still expect to see greater than 12.7v at a fast idle. Even worn out
batteries that won't hold a charge enough to start the car for more than a
couple of weeks should still be able to start it after just half an hour or
so.
Are there any bad connections in the cranking circuit? You could be losing
too much voltage to be able to start the car, even when it is charging OK
and the batteries are OK. Measure the voltage directly on the battery posts
while cranking, and again on the starter connections - you may need an
analogue instrument if a digital isn't 'settling'. In an ideal world you
shouldn't see more than about 0.5v difference, but you could see 3v or more
and this will significantly affect cranking. OTOH if the voltage at the
battery posts is less than 10v while cranking the battery is knackered or
not charged.
PaulH.
----- Original Message -----
> Well, after driving it about an hour Sunday, I tried starting it
> last night after work and the battery is dead again. It even
> lugged a little when I stopped and started it during Sunday's
> drive.
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