How the estimate works
Large fleet studies of real cars consistently find that modern EV batteries lose capacity slowly: roughly 1.8 to 2 percent per year on average, faster in the first year or two, then settling down.
- Age drives most of the loss, so the year is the biggest input
- Mileage adds to it: batteries cycled hard lose a little more, so unusually high annual miles nudge the estimate down
- The floor matters: manufacturer warranties typically promise at least 70% capacity within 8 years or 100,000 miles, and very few healthy cars get anywhere near that threshold
The result is an expected figure for a typical car of that age and mileage, not a measurement of any individual battery.
Why a battery health check beats any calculator
Two identical cars can age differently depending on climate, charging habits and luck. A car that lived on rapid chargers at 100% in a hot climate will be below the average; a gently used car charged to 80% at home will usually beat it.
A garage with EV diagnostic equipment can read the battery management system and report the actual state of health as a percentage. That single number tells you more than any estimate, and for a used purchase it is the difference between guessing and knowing.
Assumptions and accuracy
Uses a conservative fleet average of roughly 1.8 to 2 percent capacity loss per year, adjusted for age and annual mileage. Real world results vary car by car; only a battery health check gives a true answer.
These figures are estimates, not a guarantee. Last updated 2026-07-18.