My Moulton TSR bike uses Oregon 36v 6Ah garden tool batteries and chargers:
https://oregoncordless.com/gb/product/b650e-6-0-ah-216-wh-battery-pack
https://oregoncordless.com/gb/product/c750-rapid-battery-charger/
I connect one battery at a time to the controller, using a DIY lead with...