Battery issues with gameshell

Hey so as I am helping my wife with her gameshell I just noticed I have no battery power on my device and even as I’ve charged it overnight it won’t go past 50% is there a replacement I can buy for it?

None on the official store, but check out taobao

Also, reportedly a Nintendo DS battery will work. You should be able to get them on eBay or online somewhere.

The format of the battery is the nokia BL-5C