How much to replace the BIG battery? When would it likely be required?

toyota will replace it for free if it fails before 150,000 or 100,000 miles, it depends what state you live in. i think it's costs somewhere between 2,000 and 3,000 at the moment. Most people never have to replace it, i think there was a taxi driver that got 380,000 out of his battery then someone totaled his car.

 

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Hybrid battery covered for: 10yrs/150,000 miles...whichever comes first.

Looking around the Internet, there are a lot of 10 year old Prii with the original battery. I think there is little worry. The NiMHydride battery is very well known/characterized. One reason why I opted to buy now, rather than wait a year for the release of the Prius with the Lithium battery (which has higher capacity, but not characterized to the same level as the existing battery).

 

The few replacements paid for out of pocket are often from junkyards, in which case they only cost a few hundred dollars.

Tom

 

First Numbers on Hybrid Battery Failure | Hybrid Cars

Since then, the price of Toyota traction batteries has dropped to ~$2,200.

Bob Wilson

 

If you look on ebay, you can find a low-mileage junkyard battery for under $800.