Maybe a bit off topic but I made two these "light packs" out of VW E-UP modules.
Only 10 kg, and 48V nominel (57V top), and 25AH.
Cost me less each less than 50 dollar incl the bicycle bag that i found on ebay from china
only gives me about 15 min range at 14 knots, but if that not enough i can just bring two batteries
for 30 min at 14 knots.
Going slow, with the whole family
on-board I can easily do 1-2 hours at like 3 knots.
Ofcourse there is no CAN interface from the battery
to the motor, but the motor cuts at 44V and thats 3,14V pr cell so it works quite well this way.
I charge them onboard with an 500W charger
at 2 hours.