I assume the warranty for a…
I assume the warranty for a new battery is not 8 years, because when you buy a new car it's all built into the price of the car. They're not going to provide an 8-year warranty for a battery that cost $2,000.
With that being said, I was able to buy a brand new battery from Toyota back in May of 2024 for my 09 Prius, and my MPGs are right on par with the official estimated MPGs.