A couple of years ago I picked up a motorcycle with a seized engine for $100.00.
I mounted an electric motor where the battery used to be & some batteries where the engine used to be.
I started off running it @ 36V using (3) 12V 35AH Harbor Freight solar batteries.
Then, I moved up to 48V by adding a 4th battery (& upgrading the contactor to 48V)
Next, I upgraded it to a 45V 45AH Lithium battery pack, out of a Chevy Volt.
Here are some videos of the conversion.