Braun 4736 battery replacement
Contradictory to previous post: YOU CAN OPEN IT (maybe the poster is a bit too keen on selling new handles???). Replacing the battery will require soldering though.
Put something suitable in the hole at the bottom of the toothbrush, and turn it about 45 degrees count clockwise, at the same time pushing it in slightly. This opens the bayonet, and let the bottom lid come loose. Be a bit careful: there is a (not too strong) spring pushing it down, and the part being turned holds the coil of the charger which is attached with 2 relatively thin wires.
To get access to the battery, you need to slide the internals out of the outer shell. Therefor you first need to remove the white closing/sealing ring at the top (approx. 10mm diameter, 2mm high), by gently prying it upwards wit a flat screwdriver or the like, between it and the pale blue rubber. Done that, slide the internals out buy placing the metal tip on the table and pushing the case downwards.
Now desolder the two contacts that connect the motor to the electronics board, and slide the white plastic (electronics, battery and coil) module off. There are two small retractor hooks ("barbs"?) that hold the thing in place.
Desolder battery. Replace. Assemble again.
Battery is 16.7mm diameter, 42.7mm long. That is 4/5AF size, NiMH. Marking: GLH.
Measured 1.2V (empty battery). In case you forgot to note down polarity: positive side towards motor.1
Looking for how to open it: 45' of work. Replacing actual battery: 15'. Typing this: 15'
Video of more or less similar rerplacement:
Possible replacement battery:
GP BATTERIES - GP211AFH - BATTERY, 4/5AF, 1.2V, TAGGED
4/5AF size, NiMH