V40 Max handheld battery

Hi.

Does anybody have a V40 Max hand held emulator gameboy thing? I was given one that was an Amazon return but it's missing the battery and the SD card, if somebody could tell me what battery I need to order I'm sure I can figure out the SD card part

I'm having no trouble finding 3.7v 4000mah 2pin jst plug batteries on aliexpress but it would be handy to know the correct part number/dimensions before I end up buying one that doesn't fit in the battery compartment.

And if anyone knows if the SD card is just for ROMs or if it stores the firmware too, then a heads up would be nice.

Cheers