battery ki life is, for a typical hybrid car batteries last at least 10 years with mileage remaining similar to day 1, after the period of 10 years the batteries still work "tip top" but the degradation may now be noticeable. That said, personal experience suggests otherwise as a '05 prius that was in the family for a while still gave similar mileage in 2017 (up to June) before it was passed on. meray khayal say 10 saal sirf iss liye kehtay hein kyun k minimum time itna estimate hoga, warna 11-12 saal baad bhi sahi chalti hai battery, uss k baad bhi effect noticibale hoga zyada bura nhi. this is for a nickel-metal-hydride battery, the new li-ion ones are even lighter and better as per articles on the web.