NOTE: The top edges of the board are made asymmetrically so it can only go into the casing one way. Near the Blue Circles

Games with battery backup (allowing for save games to be stored in SRAM) allow access to the battery at this point for replacement. Most of the time the battery is a button cell: CR2032.

The battery is soldered in. You will have to break it out and re-solder the new battery in.