I picked up a used one of these Daymak Tokyo this summer for just $500. Still looks and drives like new, lots of storage space, but would like a little longer range than the 35-40 km you effectively get.
So this fall I took the factory battery pack (12 Ah) out, widened the tube frame under the seat about an inch, and you can now fit four U1 size deep cycle AGM 35 Ah batteries. Three are stacked on top where the old battery pack was, and the last one in the tray behind the top one, all under the seat. I had to raise the seat about 2.5 inches, but that was a welcome change, as the original seat height was way too low for a 6'3" guy like me. It worked out great, can now go over 120 km no problem and use the max power setting all the way. After a 20 km round trip it still reads full charge after returning home. Next is a plexiglas windshield, in case I get caught out in rain.
Happy e-biking!