Depending on the schedule you,fly this is very normal. I remember when I flew glow several years ago in Advnced and intermediate, I would easily put 200 mah per flight back,into the battery. You can stay with the smaller battery if you like but charge after every third flight or use a bigger battery. Your servos with glow are always fighting to find center with the vibration of your engine, again, IMHO this is normal, and digital servos are power hungry