jchapura

Some say that the resting voltage of a 12v AGM should be about 12.8v. Look up the specs for your specific battery. Also consider getting a charging system test at a competent shop with the right equipment that's working ok. Your locale's temperature extremes may influence your battery life.

Antigravity

Absolutely and perfectly normal... Your voltages will vary all the time depending on the load and if the Alternator is actively charging, and what accessories like the A/C, or other accessories are on. The charging system generally charges the battery up to 14.6v overall and your battery will drop back down to its normal voltage of roughly 12.6~8v when not being driven. An Alternator or Charger charges the battery up into the mid 14s but then the battery drops back down to is resting/nominal voltage when your not driving. But, 12.1v when the engine is off would be low... but maybe you didn't drive for several days the the battery was drained a little from the parasitic draws of your vehicles system when not driving.

You will get flags, or the car won't start well when the batteries are failing.... this indicates it's not holding a charge. Lastly, you should actually be keeping your car on Porsches charger if you are not driving often enough to keep it in a good state of charge. Oh yeah another last thing... don't let you batteries over-discharge to point of needing jump starts below about 8v the battery can get damaged and below that and the longer you leave it there the more damage to your battery and that is why it won't last long.... coupled with the fact that they are not making Lead/Acid Batteries to last long nowadays, they want recurring revenue.

patentguy

Thanks.