What sells in your country could be very different than what sells here in the U.S. for example. I'm assuming you're going to start with local sales, as shipping ebike batteries is very complex. So I'd try to find some clubs or forums in your area. When you're ready to branch out and sell to other countries, do a lot of market research (obviously you are already on that) and develop a solid business plan and see if you can get some investors based on your local sales. Good luck, I wish you success, I love to see young people following their passions.