Not sure if others have seen discussions about the Walmart Ebike. I bought one recently and just put it together.
Walmart E-zip? - Bike Forums
Check it out. When it was in stock it was $300. Bicycle, electric motor, everything.
Walmart E-zip? - Bike Forums
Check it out. When it was in stock it was $300. Bicycle, electric motor, everything.

).. so, I imagine It would be pricey to replace just the stock batteries.