It seems that the battery of my kid’s box is getting old. The box shuts down after about 2.5 hours of playback (used to last much longer). So I need to replace it. Is there anything that I need to watch out for?
Also: does it make sense to replace to battery with a larger one (more mAh)? If so, what are the pitfalls of such an endeavour?
Stick to nimh and do not let you mislead biz the biggest capacity, expect that this is not the actual one.
If you are able to solder, think about using 3 eneloops and the cables and the resistor of the old one, but don’t ask me for details.
But I’d need details if I were to do the second option. 
Can anybody else elaborate?