You can try another kernel. I'm using siyah kernel, it gives me pretty decent batterylife and performance. Also, try using the setting force gpu in developer options, it may decrease cpu load.
Install siyah kernel, download extweaks app and under misc settings use reset fuel gauge. Recharge your phone after a few hours to 100% and you won't get any drops... I've had similar drops before, but haven't had any since.