From the first days when hybrids hit American roads in 2000, consumers have worried about expensive battery replacement costs. But reported cases of hybrid battery failure have been almost impossible to find. Suddenly, in the last couple of days, there were two posts in the HybridCars.com discussion forum from hybrid owners with battery woes.

Kayhud wrote, “I have 150,000 miles on my 2001 Prius and now need a new hybrid battery as well as the battery that controls the computer. The price is $4,000 – $5,000 in parts and $1,000 in labor.” Kayhud is considering the payment, if new batteries will buy another 150,000 miles for the six-year-old Prius.

StuckeyC37 wrote, “As I was driving home the other day, the IMA light came on my 2003 Civic Hybrid. I took it into my local Honda Dealership. Of course, they said the battery pack needs to be replaced at a cost of $4,500.” StuckeyC37 is leery of the dealership, which doesn’t have a great reputation for honesty and for correctly diagnosing problems. (We’ve reported on some dealerships which replaced the entire battery pack rather than fixing the faulty battery connections.) MSantos, a regular contributor to the HybridCars.com forums, wrote, “It is almost common for first generation Honda Civic Hybrids to undergo a battery replacement as they approach and exceed the 100k mile.”

Toyota offers a 100,000 mile warranty on emission components and the hybrid battery pack, and Honda offers an 80,000 mile warranty on the same. In California, warranties on the hybrid batteries are extended to 150,000 miles.

The real-world experiences of owners with first-generation hybrids—now clocking mileage into six-figures—will be the real test of the longevity of hybrid batteries. And the commitment from carmakers and dealerships to respond to any bona fide problems.