Re: model airplane engine?
Welcome to the forum. What you need depends on how far you plan to ride, among other things. Commutes of 5 miles one way can be done with SLA batteries. Longer commutes require better, more expensive batteries (like LiFePo4 or metal hydride). You can store the electric bike safely inside the store or office.
I used to commute 50 miles round trip to work when I lived in the Phoenix area (with a 48cc China girl). The cost for an electric bike that can make a 50 mile round trip would have been far too steep for me.
“You're only young once, but you can be immature as long as you like" -Unknown