JK98 wrote:
Don’t do it! You may end up with two broken players. The Fuze is not easy to open and reclose. The player was not designed for ease of repair. Leave good enough alone, and be happy the two players are working. Don’t try to fix what isn’t broken.
The OP never said that both players were working. They are also different memory size. It’s possible he bought a DOA 4GB unit strictly for the pristine casing and just wants to give his 8GB unit a face-lift.
It’s certainly possible, given the correct tools and time spent googling and pouring over all the photos & tips others who have done the same thing have posted all over the net. On changing out the battery? That depends on the use and age the 8GB one has on it and whether the battery in the 4GB player would actually be any better or not.
Then there’s always the ‘tinker’ factor. “I’m in here already. What else can I do?” 
