I had a friend at work who drove a 2001 Prius to about 233,000 miles. He knew I owned two Priuses and a Camry hybrid so we talked about hybrids all the time. He was in the electrical maintenance shop at work and I trusted his input. He kept up to date on hybrids and told me he had never heard of any Prius batteries failing. Knowing that such a thing was, indeed, possible, though, he also found that there are outfits that can replace the battery packs for a fourth of your stated cost. I do not know that to be true, but it could be worth study. My two Priuses are about halfway through their 100,000 mile battery warranty.