2008. 300,000 miles. Second alternator. Car is not driven much, mostly sits covered. Had to charge the battery because it was at 11.97 volts from sitting. Full charge at 13.2. Car started right up, but the output was at 13.6. Did not matter if it was just idling or idling with everything on (a/c, lights, radio, etc). Last time I checked it, output was 14 something. This time, rock solid at 13.6. Turn the car off, 13.1. Output seems low.

 

It looks like you're checking the battery voltage right after you switch the engine off. Wait a few hours and check it again. You'll probably find it's closer to 12.6v with engine off. When you restart the engine, wait a couple of minutes for the engine to settle to a steady idle before you check the battery voltage again. As long as it's at least 1v more than it is with the engine off, you're fine.

 

You are right. Letting is sit overnight removed the surface charge and today the battery was 12.7. Engine idling was 14.1. All good. Thanks