Generally, Pokemon games before the GameBoy Advance era had SRAM and a small coin cell to save state as NVRAM (Non-volatile random access memory) was more expensive. These coin cells last 10-15 ...
Changes to the data structure between Generation II on the original GameBoy (Pokémon Gold, Silver and Crystal) and Generation III on the GameBoy Advance (Pokémon Ruby, Sapphire, FireRed ...