Quick update after I took a long break from this project.
I would like to retest this bike at 60 volts, but first I need to install a much stronger freewheel.
I managed to grind down and remove the motor linking sprocket, found the previous destroyed freewheel, and remove it from the freewheel adapter.
So next I need to
1. Order this freewheel
Sick Bike Parts
2. Attach a sprocket to it at the right spacing
3. Install it on the freewheel adapter
4. Make a replacement motor-link sprocket
5. Reconnect chain drive
6. Swap out the battery charger
7. Reinstall 5th battery