Dead battery - Is the alternator bad?

[Ian c]

Just had a quick look on your local CL ...
This would be more than ideal for 75 bucks if it has leads etc .

fluke multimeter

Or this one for 100 .

http://sfbay.craigslist.org/pen/tls/4043200302.html

This one is older , but cheaper . At 60 bucks

http://sfbay.craigslist.org/sfc/tls/4047183659.html

[3point2]

Helpful posts! Thanks!

I just checked voltage with the car off and it's at 12.2V. With the car on, it's 14.3V. So does that mean the alternator is good?

I'm starting to suspect that something is draining the battery from somewhere. When I was driving the car the last time, the radio went out. Now with the battery charged up it works fine. When the car sat for a few days, the battery was completely dead.

Any other thoughts?

If it was the voltage regulator, the voltage would be showing up all over the place on the multimeter with the car on, right? It holds a steady 14.2-14.3V with the car on.

[Ian c]

It is within range but how long did you leave it running for ?
it could drop off after a while so put your lights on and keep it ticking over for a while .
what meter did you get.
This type of scenario is why i use flukes with min/max and logging etc.

next you need to disconnect the ground and put your meter across battery- and disconnected - clamp wthen close everything .
This willtell you what your drain is running at .

[3point2]

Ok. I just restarted the car and the voltage is now reading 13.9V. Voltage is going down slowly even with the car running.

Sorry Ian. Don't quite understand. Do I disconnect the ground while the car is running and then check voltage?

[Ian c]

Sounds like the regulator and or alternator is going .
It should read steady with a small load on it like lights on .
Everything else turned off , and don't forget the hvac controls ...

The drain check is with everything off to take an amp reading of what you lose from the battery with the car turned off . (Ie: parked over night)

[3point2]

I left the car running for 15 minutes and with the headlights on. Voltage got to as low as 13.48V. Then I turned off the car and the battery is at 12.5V which is slightly higher than earlier i checked.

Ehh electrical gremlins are the worst.

[Ian c]

Them figures are t the end of the world .
It dropped but still was high enough to produce a charge for the battery .

Did you get a meter with dc amps ?