I need help to my hack waterproof MP3 player

[CrackpotHead]

I bought a cheap water proof MP3 player on ebay (Blue Swimming Diving Water Waterproof MP3 Player FM Radio Earphone 4GB New | eBay). I would like to modify it in two ways.

First I think the battery is crap. It dies after 30 minutes after a month of use. I would like to pimp it out with a lithium ion rechargeable battery.

Secondly, it plays only mp3 and wma. I would prefer that it play mp3 and AAC.

My main problem is that I have no idea who makes it, and what kind of firm ware it's got and I can't even figure out how to open it..

I'm new to this but I'm not afraid to flash firmware and do a bit of soldering.

Any help would be much appreciated

Cheers
CrackpotHead