Just google. "Prius, "battery" and "lifespan". You'll see they will be the last component to go (lasting up to 400.000 miles).
Here in Belgium, Toyota gives longer warranty on the hybrid components (8 years) than on the rest of the hybrid car's components (5 years).
The only way to damage the Prius/Auris/ct200h battery is running the car on an empty fuel tank in pure EV mode, until it completely dies on you. Such recklesness wouldn't be covered. Otherwise, no worries with the battery's lifespan and the corresponding warranty.
I agree with the posts above. I've seen articles on the exceptional reliability of the Prius as used in Taxi fleets in major cities like in Vancouver, NYC, etc. These drivers have recorded 250 000 miles or greater without any failures in the hybrid mechanicals.