Yes, you can replace the battery on a Leaf. Mine is 3 years old and it still has full battery capacity at this point. The new batteries cost almost as much as buying a used Leaf. (About $9000 USD) It can be done yourself, but the batteries are really heavy and come in a very large pack. So usually it is done by a Nissan shop mechanic. I'm still waiting for a third party battery manufacturer (or someone who will rebuild an old battery pack) for cheaper than a new Nissan battery.

I've also seen replacement batteries for hybrid cars such as Toyota Prius. These have been around long enough that you can buy a third party manufactured battery and they are a LOT cheaper than Toyota's factory battery.

It's interesting that for the Tesla, they are considering a battery "subscription". They are really easy to change out (it's the whole bottom of the car which just unbolts), so you basically just drive away with a new one when your old one dies.

If I had one of those electric scooters, I would look into replacing the battery and charger myself. You probably can get it a lot cheaper if you are not afraid of doing a little research and getting your hands dirty. It sounds like they are buying cheap Chinese batteries and chargers and marking the price way up.