The fixed Gen 7 ROMs consume more battery than original games because they push the GBA’s CPU harder. On an original GBA with a backlit screen, expect roughly 4-5 hours of playtime.
If you see a website offering a "Pokemon Gen 7 Gba Rom Download Fixed" that requires you to run an installer, close the tab immediately. It is likely adware or a virus. Pokemon Gen 7 Gba Rom Download Fixed