Finding a battery is tough. I'm not sure which ones work. This one specially made up by BatteryWorld (Melbourne Australia) for $26 FAILED later. If you find a better solution let me know.

Phillips has designed their product with a battery enclosure that is approx 1mm too short to fit the standard size AAA batteries. In my opinion, designing with built-in obsolescence like this should be a criminal offense.

You're looking for two Ni-MH AAA-sized batteries with at least 750 mAh each. Eneloop and Eneloop Pro work well and can be found on Amazon.