going from what the packaging says on this page for the voltage:
https://info.sonicretro.org/Amazing_Sonic
and taking the size into consideration they look like they could be a 357, also known as a AG13, also known as a LR44... coin batteries have lots of names for the same size...
edit:
the instant i posted i went to close that tab with the link above and noticed they have a manual scan and it does show AG13 in the manual so yea a battery with any of the numbers listed above, they are all the same size and voltage