That's not entirely true, from what I read they had a small percent of the real gen1 Prii with battery problems in Japan, but that was to be expected in the shake-down model. The 1997-2000 true first gen (Japan only) Prius used a pack of real 'D' cells whereas the 2001-2003 models used a much improved rectangular cell system, and those have never needed any replacement, nor have the 2004-2005 models, but I wouldn't expect anything to go wrong with them yet. Overall reliability is extremely high, given the numbers of cars on the road all over the world.