Although this is not a wiring diagram, this video may help you figure it out. I can't tell for sure, but it looks like there may be 3 separate battery connections. The connection in the forground is the internal jumper that connects the two 12 volt batteries in series to form a 24 volt battery, and the background connections are to the mower circuitry with positive wire on top and the negative wire on the bottom.
https://m.youtube.com/watch?v=IhLs756ZZTw
the motor black lead as well as the battery black lead connect to the same point on the circuit board, a hole in the corner that requires a through bolt and a self locking nut.