Stay well away from that ebicycle.
You won't be able to find any eparts for it, it probably wont be covered under warranty. If you can find parts for it, the parts will be extortionately high.
Any used battery, is worthless. Its a proprietary system, you need their battery unless you can find a hack for it. You have no idea how the bicycle was taken care of, stored in -30 weather all winter, then in +105 all summer = not good at all. If it was under water, not good for battery neither, even if it still works. So many unknowns, thats why stay well away from used batteries. Safety FIRST! The battery is the most expensive part of an ebike, motors and controllers can be had for cheap.
You want to get into ebiking for cheap, install a ebike kit on an existing bicycle. Pretty simple, plug and play systems out there. One stop shop, battery, charger, ebike kit. Slip on the hub wheel, zip tie controller, slide on controller. But some cant hack that.