How to replace a GameBoy cartridge battery without losing saved data
Amazon.com: CR1616 Batteries with Tabs,12 Pack CR1616 Lithium Replacement Save Battery for Nintendo Game Boy, GB Color, Advance and Pokemon Games : Video Games
Pokemon Emerald Battery Help : r/Gameboy
Pokémon Sapphire - "Battery has run dry" after replacement of both battery and crystal : r/consolerepair