we need to change batteries every 2-4 years
Wait, what‽ No. We don't need to change batteries every 2-4 years. That's what you do with TV remote controls and temperature sensors, not electric car batteries, LOL!
Electric car batteries are made to last at least 7 years (from a warranty standpoint) but in reality it's more like 10. Not only that but they're not single, gigantic objects. They're made of lots of "cells" so if one of them is going bad you can replace just that one bad cell.
Anecdote: The batteries in my Prius lasted 15 years before I had to replace one of the cells. Then a year later I had to replace another one. A year after that I sold it so I have no idea how the batteries are doing right now but I'm sure another cell would probably need to be replaced by now 19 years in service).
I'd also like to point out that the latest electric car batteries are vastly superior to the ones in my Prius.