My unit was originally from the UK (there it went by the name Philips TT2040), but the innards were exactly the same.

Used a pair of old (Sanyo) AAA eneloops. It took a bit of force to get the batteries in place (as noted, they felt a bit oversize, but I wasn’t sure if it was my shoddy soldering, or the actual enclosure size). On the first try, the module was not aligned properly - I was getting 8 orange flashes on button presses and no reaction on the charger. Once I managed to insert the module correctly, with all the pins/slots touching correctly, it started working like a charm.