The mainboard battery for the deck is a flat topped AA - at a squeeze you can push fit a standard rechargeable AA (NiCd or NiMH) - they will actually go in, just persevere - I have fitted to six of my units. The flat topped versions are available on ebay.
The Lip8 carcass contains a standard 14650 battery - just open the carcass along the seam (there are a couple of self locking tabs) - carefully remove the old battery by pulling off the tags with pliers and insert the new one - no need to solder, the battery will make contact well enough to work properly - reassemble the carcass and that's it. Lip-8s are almost impossible to find.