Questions about battery/alternator voltage


Founding Member
Apr 30, 2000
I have a gauge that tells me the volts when the engine is running and the battery voltage when resting.

I wanted to know if it is normal for the alternator to put out 12.2 - 13.3 at idle at a light from time to time and then go 12.5 - 13.5 with only the a/c running in the daytime? (non-electric fan)

Also the battery at rest (engine not running) will go from 12.5 - 12.2 with nothing on ?

The car starts fine and would not suspect a thing if it was not for the gauge.

Do i have a bad battery or am i concerned over nothing?

Anything you can tell me about batteries and alternators would be helpful!!
  • Sponsors (?)


"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
If you have the stock 2G alternator, that can be normal. Some basic guidelines:

With the car off, the battery should be around 12.6 volts (this is the break-even point for the charging system. A voltage reading of more than this = charging. A reading of less = discharging or draining the battery).

At start up (cold idle) look for 13+ volts.

At hot idle with an accessory on (this is a 2G joke), it can be normal to see volts drop below 12.6. If this occurs for short periods (e.g., sitting at a red light), most dont mind it. You just wanna see more than 12.6 volts once the car is moving.

A 3G conversion would help this issue, but if you dont mind it now, it is not a huge deal.

Underdrive pulleys (if you have them) dont help, as they slow the alt down.

Random thoughts. Good luck.