seeking list knowledge - auto electrical

Huw Powell
Tue, 27 May 2003 13:59:28 -0400

> I'm helping a friend troubleshoot an electrical problem in his (non-Audi)
> car - it's a plymouth laser - NAC but it is a turbo ;)
> Anyway, he just put in a new battery3 weeks ago, and about a week ago he
> started getting slow cranking at all times, and occasionally would not even
> start, even after just being shut down from a short drive.
> I put the DMM on the car and found this.
> Voltage at the battery (car off) is about 10.5
> Voltage at the battery (car running) is a steady 14.3
> Shut the car off and voltage drops right to 12.5 and then starts dropping at
> about 1 volt every 2 secs til it gets to about 10.5
> Shut the car off, disconnect the battery and voltage shows steady 12.5

that sounds like a dead cell in the battery.  it takes *some* draw to
remove what little charge that cell holds, though.

Try the battery in another car/another battery in that car.  Or at least
try charging it, removing it, and running a light bulb for a few
minutes.  Remember, a healthy, or even decent old , battery can run the
interior lights and windows after the ignition is off, power lock the
car, then later power unlock the car and run all the seat belt etc.
bells, *and* start the car, all before being recharged at all.

> Assumptions:
> Charging system is good
> Battery is good
> There is a short somewhere that is causing a current drain.
> The car does have some fancy dancy alarm system that may or may not be
> working properly as well as a very involved stereo system (2 amps,
> isolators, etc).  I think the alarm system is a likely suspect.  My friend
> bought the car with it already installed and doesn't know anything about how
> it's wired.
> With the car off and key out there is about a steady .14 amp current draw.
> Does this seem high?

Yes, but it shouldn't be enough to kill a new battery that is getting
charged at 14.3 volts that quickly.  IMHO...

Huw Powell