There is a pretty good disucussion on this topic in a previous thread.

AMG Batteries charge and discharge, check it out, but just looking at your #'s they are close to ours and if I had to guess I would say that 26.5 you get when plugged in is reflecting the charger on.

I try to not let them go below 24.5(resting) and the highest I've ever seen them go while charging is 29.5.