Gas to Amps (just for rythm)

>>1200482
The best value for ebike batteries are the HobbyKing 4s 4ah hardcases at ~$25.
Electric motors both spin too fast and lack torque - so figure out your gear reduction first. The smallest pulley should be ~14teeth to really grab well which puts an upper limit on single stage reduction. Look into jackshafts to get another gear reduction in the same space.
The freewheel that came on your bike probably sucks - look into replacing that.
Honestly, just buy a BBSHD kit.
and visit 'endless-sphere' before buying something shitty

>>1200482
Tell us how it goes. I like my 66cc engine because its quick as shiy and looks like a 49cc. I like the idea of electric but dont have any experience.

Lots of tech for ebikes now, and lots of kits - both middrive and wheel hub. The former are much better in hilly areas. I'd suggest buying a kit, it's the easiest way.

As for batteries, use lithium packs. (18650's are safest). The kit should be 36 or 48 volt if you want any power at all. DO NOT USE LEAD ACID - their weight is far too much and the discharge plane means you start losing power before your battery is even halfway discharged.