So I did a little more research and this is what I found about the Prius battery.
1. It uses a nickel metal hydride battery, not a lithium. My bad.
2. They do maintain a charge of about 60% as apparently this is the battery's "sweet spot."
3. Since the Prius has come out (2000), Toyota has not had to replace a single battery for wear and tear.
Following links are where I got the info:
We are giving away 'Black Panther' swag!
Four lucky readers will be taking home *Marvel*ous "Black Panther" prizes, including magazines autographed by the King of Wakanda himself! Giveaway ends Feb. 25, 2018.