Optima red top and Subaru charging system

[WhyMe]

I have an optima red top in my 99 outback. i put it on a charger every once in a while to bring it up. if i leave it overnight it gets to 13.1-4 volts and stays there. After i drive it a few days it settles at 12.4 v. charging system is putting out 13.5 -14v.

I have never owned a optima before. So why the drop in voltage? is it normal? I only use it for starting the car and the oem accesories. is parked in a garage.

 

[JHZR2]

A battery is fully charged around 12.6V. Charging system voltage must be higher to overcome resistance. Even when fully charged, batteries can be "floated" at an elevated voltage to keep them at 100% and prevent self-discharge which can occur.

 

[HTSS_TR]

I have a Schumacher automatic charger SC-7500A, it shows a fully charged battery at 12.8V. It has a maintenance/float mode and it keeps battery at 13.1-13.3V after fully charged.