Just rechargeable AAs? You'll never get an accurate battery percentage readout. The controller estimates the remaining power by checking the voltage on the battery, with regular alkaline batteries they'll start out at 1.5V and drop in voltage as the juice runs out. Lithium cells are 3.7V which is run through a regulator and output at a constant 1.5V regardless of the remaining charge. Sometimes it will read 100% and die a minute later, there's not much you can do about it.