Bad alternator? new battery reads 12.3 volts

Camry 4cyl. Sears Diehard Gold, while running it reads 12.1 with my small multimeter.(12.3) with engine off.Two semi experts told me it should be 14 volts.what do you think.I’d like to test the alternator w the meter but don’t know where to touch the contacts.Electrical is my weakest area…thanks for your help…Mike

A fully charged battery should read 12.6 volts with the engine off. The reading of 12.1 means the battery is run down a bit or is bad.

Start the engine and do a preliminary test across the battery terminals. (black lead from the meter to the negative post, red lead to the positive)
Engine running and preferably with all peripherals off (lights, fans, etc.) you should see around 13.5 to 14.2 volts.
This voltage varies due to the electrical load the car is placing on the system.

Measure the voltage with the engine off. Then have someone start the car and observe the meter. Have the driver rev the engine a little. The voltmeter should slowly climb towards 13 volts, then after a minute or so be up to 13.6-13.8.

If the meter stays below 12.5 volts with the engine running at fast idle, the alternator is not putting out…Most of the time, an alternator failure will trigger a red dashboard warning light, “alt” or “Batt”…

I assume this is a 2004 year Camary. In addition to the checks previous outlined, check the 120 amp ALT fuse in the under hood fuse box. I assume you are getting a BAT light on the combination meter when the ignition is ‘on’ but the engine not running.

Hope this helps.

It's a 90 Camry, but thanks for your help ....and "Caddyman and Ok - always a pleasure to hear your sage advise.My old alt. was charging at only 12.1 but the "CHARGE" light on the dash never lit up(except turning the key before starting) Last night with a new Diehard and new alternator (which read 14v while charging) I was happy....7 am - battery dead. Since I ran it only 5 minutes after installing, I guess I have a short. The last year I sometimes see the "LIGHTS" light on the dash light up) and I'm pretty sure it's the licence plate lights. I had to jiggle the small harness wire taped to the trunk hinge arm to get it to pass the safety check. I had been treating rust in the spare tire well.  Could the trunk light drain the battery overnight ? If I take out the bulb it wouldn't use any power would it?    Mike

Could a trunk light run a good battery down overnight ? thanks, Mike

Yes…Those are pretty bright lamps, probably pull 3-4 amps. Four amps times 10 hours equals 40 amp-hours, which will pull most starting batteries way down…If the battery is very low, you are better off to charge it on a battery charger and not ask your new alternator to do it. Todays alternators do not take kindly to charging dead batteries. Theoretically they should be able to do it, but experience has proven otherwise… It’s just too big a load for them.

Thanks Caddyman, I was a bit surprised a while back when told of the hazards of charging a dead battery with the alt. It was so logical and yet at my age I hadn’t heard of it. The Napa guy told me as I took the alt… and hear I thought I knew all the basic stuff. In a pinch I suppose you could give it 10 min w the good battery (jump car) then drive 10 min and park to eat or shop while the alternator cools down. would that work ? Good thing I bought the Checkers (usually I steer clear except for fluids) which was $120 and lifetime warr. - Napa was $170 with only 3 yrs warr. … Mike