I do not think we have had any Prius v NiMH batteries replaced yet. That's a good thing! Question comes up on another thread, I wonder how much USA Prius v NiMH battery cost compares to a Gen2 or Gen3 batt? Question #2 how about cost of an EU Li batt for Prius v (assuming EU has Li batt)? ...and of course how about Gen4 NiMH v. Li batt cost? but I think the Gen4 answer is that the HV batt cost has not yet been published.
According to the Toyota tech manuals, the part number is G951076010. A quick search looks like it's around $2200 USD, plus install of course. That's actually not too bad - I'm not too sure what the cost difference is between the 2 types of Prius, maybe it's the same battery?
If I need one someday, I will go to "rebuilder / reconditioner" who can swap out the battery for less than half the price on a Gen 2. I am sure when more Gen 3's are available they will cost less rebuilt. Rebuilt Batteries | Hometown Hybrids
