What I did was clone the smaller card to the large card (format the large card first) with Balena Etcher. That creates a perfect image on the new card, but locked to the original card’s size. To fix this you just pop the SD into the PC with a card reader, open the Batocera folder, and in batocera.conf uncomment the line ‘autoresize=true’.
Plug the card back into the Pi and it will automatically resize the partition to use all available remaining disk space. Nice n’ easy, and relatively quick!