Game Boy and Game Boy Color games use a CR2025 or CR1616 horizontal mount "Surface Mount" battery (CR2025 batteries will normally fit fine in games made for a CR1616 battery and will last longer) Game Boy Advance games use a CR1616 horizontal mount "Surface Mount" battery and will need a "triwing" screwdriver to open them. Most non-portable console games use a CR2032 horizontal mount "through hole" battery but it is worth having a look before you order anything.