Just play on an emulator. Save states anywhere you want.

Pokemon Emerald's battery is only there for real time clock functions. Saves remain intact even after the battery runs dry.

Gen I and II games used the battery for save data, however.

It sucks when you borrow a friend's SNES and didn't realize that was a problem and their saves suddenly disappear (along with your current playthrough on a different save file) and you worried you somehow did something to cause it.

if I slap E.T. into that son of a bitch, it plays.

But why would you do that?

the og atari and nes were video game consoles.

a 'modern' console is just a required hardware device to access a subscription service and game rentals falsely advertised as purchases.

My only dead battery so far is Final Fantasy NES!

I have a Rev B gold Zelda cart for NES and I am curious its battery state. But my NES was lost in time.

I'm mostly referring to completed saves of Kirby and DKC-franchise. The first is a collection of games you have to unlock, so if you just wanted to play in the arena mode, then you'd have to play through a whole lot more just to unlock it.

Nearly every cartridge-based system up to the 3DS saves to the cartridge. But many older cartridge games from that era (SNES, GBC, sometimes GBA) used volatile SRAM that needs to be constantly powered with an internal battery. When the battery dies, the save is wiped and it can no longer hold a save, though you can always open the cart up and replace the battery.