Hey guys,
So I finally went to the beach for the first time since getting my optima yellowtop battery, and was using my truck as the boombox(as usual) with the engine off. Well i noticed something VERY strange...
Typically ill start my engine every 30 minutes or so just to be safe, and i did this as normal. I was playing moderately loud music for about 1.5-2 hours. Well with my typical batteries (NON AGM) (autocraft gold), if the battery is gettin low, obviously it will crank over a little bit slower, but if you watch the gauge, once the engine is running, it reads out anywhere between 13.8-14.4 volts. Well this time with the optima,(before leaving) i had my ignition on, but engine off, and i noticed the gauge was right above "12", so i though that was strange, but if i start it it will go back up to ~14.4 in a few seconds. So i started it and observed, it cranked over just fine, that the gauge stayed there right above "12", i let the engine idle for about 2 or 3 minutes and noticed it hadnt moved up at all. so i gave it a few steady engine revs, and little by little the gauge started moving up towards "~13 V". Very Very slowly. I continued with a few steady revs, and it went up a little higher, but right around ~13 V it wasnt going up much higher at all.

So my friends and I were leaving at this point, and i figured driving back 5 miles down the beach and then getting on the highway my gauge would charge itself back up eventually, but by the time i got home, it still had hardly risen above ~13.5 V.

The next morning i got in my truck to go to school and the gauge was back to where it was supposed to be "~14.1-14.4 V".

Is this a normal process for optima batteries?
I am new to the AGM style, when they drain down a little bit, is the recharge process longer?
Just wondering is this is a problem, or is this something i now have to get used to?
thanks for your responses!