Battery replacement depends on the state of health of the battery. Our warranty is 3 years, unlimited km, and 70% state of health. Our testing shows that even at 60,000 km, the state of health remains over 85%. For our earliest Ather 450 owners (2.5 years old), the battery state of health is on an average above 90%. So the batteries should be easily usable for 5-7 years or even more.