Wanting to get started with NES repros

[scarmullet]

Ok, I recently got access to a EEPROM burner and I thought; "hey, maybe I can make some repros", but I realized that it may be a little more difficult then previously pondered.

I know about mappers and all that, but what about doner carts for some games, like is Super Mario Bros 2 with all pins the only cart you can use for Final Fantasy 3? Why cant you use Deja Vu, Shadowgate, Base Wars: Cyber Stadium Series, Baseball Stars II, Crystalis? They all use the same iNES mapper, MMC3B mapper, WRAM and Mirroring, and they are all battery save so you dont need to add a battery holder.

[scarmullet]

Ok, I just found out that using those games, it can be done but you would need to add an enable pin to the CHR RAM chip, how does one do that? Or how does someone add in a battery holder to a SMB2 cart for conversion?