Charger
MDA Li-ion Battery Charger
This is the battery that ships with the original bike.
Manufacturer: https://www.mdacharger.com/
Model: BC254480030
Input: 100-240V ⏦,2.5A (max) 50/60Hz (Alternating Current)
Output: 54.6V ⎓ 3.0A (Direct Current)
Back of the Unit Notes:
Red Light when charging
Green Light when fully charged
Cable - 18 AWG
Connector - 3 pin with a proprietary connector
Center pin looks unused
Lower Left pin is Negative
Lower Right pin is Positive
Modification
A guide for modifying the charger, and optionally the battery itself, to work with Grin Technologies Cycle Satiator: https://www.reddit.com/r/Super73/comments/invi7q/upgrading_to_a_better_charger_a_guide/
There's a relevant quote in the guide regarding the center pin:
We only want the red and black to be terminated properly as the Yellow Signal wire is not really used for anything inside the battery pack itself.
An original charger box with cables and safety manual.
Detail of the cable, including the American Wire Gauge size (18 AWG).
Detail of the connector that mates with the battery.
Back of the charger, including the connector diagram.