Sansa clip replacement battery; where to get?

[may]

One urban fox nicked 2 of my 8 Gg sansa clip from my pc desk & took to play in the back garden, one of them is soaking wet from rain as I only found it few months later; it is still working but battery doesn't charge

I want to try replacing new battery instead of throwing it away; I have 6 sansa clip & clip+; just love them, so I want to learn replacing batteries for them.

Any one has a link of where to get the battery? I am in UK

many thanks

May