Diagnosis Help Needed: Battery or Alternator?

[Earl_H]

Had the Viper out yesterday after about 2 weeks of inacticity. Drove it to the gym (~ 20 miles) no problem. On the way home the battery voltmeter went to 0, the rpm guage went dead, the radar detector started to pulse off/on, radio eventually went out. Then the battery light came on. Got the car home, turned off the ignition. Tried to restart but the battery went dead. Put a recharger on the battery for about 3 hours and then sucessfully restarted the car. Does this sound like an alternator problem or a battery problem?

 

[Earl_H]

Let the engine idle for about 15 mins. and the volt meter went to 0, car still ran.

 

[luc]

make sure that your battery connections are tight and connect a voltmeter whith the engine idling.
Volts shoud be above 13.5/14.
If not, problem is with your charging system.

Luc.00GTS

 

[Earl_H]

Strange thing...AEM reads about 9.5-10volts. When I use a voltometer it pegs at 15v.

 

[Randy]

One way to test - disconnect the battery at the engine compartment battery connection and put a charger on it (the battery cable, not on the connection to the car ). Let it sit on the charger for a while (a number of hours at least), then disconnect the charger (leaving it disconnected from the car), and let it sit some more - overnight perhaps. Then re-attach it to the car and see if it will start the car. If it starts the car, meaning the battery is accepting *and* holding the charge, it would seem to be the charging system. If it won't start the car, its likely the battery. Or, you can take it to a place that has a battery load tester and save a bit of waiting time.

 

[Earl_H]

Turns out it was the AEM, replaced Alt. and Speedo for nothing...well it was a good exercise in learning more about the Viper electrical system. Live and learn.

Thanks to all that offerred help on this (especially JD).