electrical power failure in 2005 Forester

[joyron]

This happened last night. My wife stopped the car which had been
running fine all day with many stops, and starts. When she went to
start the car, there was no power at all, not on dash, and not even a
"click" when she attempted to start the motor. She called me, and I
went to where she was, maybe 20 minutes or so later. When I got
there, power was restored somewhat, dash lights on, and headlights. It
did turn over, but as if the battery was drawn down, and almost dead.
I put a jump start on the battery, and it started right up, and she
drove it home. No alternator lights came on. This morning, it
started right up. I checked the voltage on the standing battery, it
was 12.9 volts. I checked the voltage running, and it was about 13.8.

I will have the car checked out by my mechanic, but I am wondering if
anyone has any thoughts about what this could be?

TIA. Ron

 

[johninky]

Loose battery cables/corroded battery post/bad battery ground.

 

[VanguardLH]

This happened last night. My wife stopped the car which had been
running fine all day with many stops, and starts. When she went to
start the car, there was no power at all, not on dash, and not even a
"click" when she attempted to start the motor. She called me, and I
went to where she was, maybe 20 minutes or so later. When I got
there, power was restored somewhat, dash lights on, and headlights. It
did turn over, but as if the battery was drawn down, and almost dead.
I put a jump start on the battery, and it started right up, and she
drove it home. No alternator lights came on. This morning, it
started right up. I checked the voltage on the standing battery, it
was 12.9 volts. I checked the voltage running, and it was about 13.8.

I will have the car checked out by my mechanic, but I am wondering if
anyone has any thoughts about what this could be?

TIA. Ron

http://groups.google.com/group/alt.autos.subaru/browse_frm/thread/b28661db9021fc4b/8b0bd3fd66d002d4

See johninKY's reply where he mentions the battery draining back through
a defective diode in the alternator. I have replaced 2 bad alternators
(on 3rd one now) and never did an idiot light come on telling me the
alternator had failed. Of course, the drain occurs while the car is off
since the alternator is putting out a higher voltage than the battery.