Well I have decided on a single 18650 lipo cell (Protected). I really don’t think I can fit 2 in. I have sourced a dc-dc Step up board and I have also found a little 3w amp board
3V to 5V 1A DC-DC Converter Step Up Boost Module NEW
Mini 5V Digital Power Amplifier Board PAM8403 Class D 2x3W NEW
I found some 8 ohm speakers cheap from HK that will fit nicely in the Game boy.
1W 8 Ohm 28mm Round Metal Shell Internal Magnetic Speaker Replacement 4Pcs
I have found a company in the UK that sells the lipo packs
I’m planning on charging the cells externally If I can get them out it may be a little tight as they are 68mm long. Failing that I can still use 4 AA rechargeable cells to test it prior to getting the lipos.
XTAR MC1 USB Li-Ion BATTERY CHARGER 18650 18500 18350 14500
2x Torchy (Panasonic Inside) 3400mAh Protected 18650 3.7v Li-ion batteries
I found an interesting build that used wire for the button input pcb contacts I may try that and buy a reel of 24k gold plated wire.