The SUPER73-MZFT seat bucket is not large enough to store dual 3P batteries and can only run a dual 2P battery configuration for this reason.
Never use two different sized batteries at the same time. When running a dual battery configuration, ensure both batteries share the same model specifications. (2P+2P or 3P+3P only)
Single Battery Configuration
Compatibility as a standalone battery by model
2P Battery (520 Wh)
SUPER73-MZFT
SUPER73-MZFT SE
SUPER73-M1D
SUPER73-M1D SE
SUPER73-B1G
SUPER73-B1G SE
3P Battery (780 Wh)
SUPER73-MZFT
SUPER73-MZFT SE
SUPER73-M1D
SUPER73-M1D SE
SUPER73-B1G
SUPER73-B1G SE
Dual Battery Configuration
Compatibility as two batteries used at the same time by model