Formula
Health scales the pack. The buffer then removes a share of what remains:
usable kWh = nameplate × health × (1 − buffer)
The range page multiplies usable kilowatt-hours by miles per kilowatt-hour. This page stops at the energy.
Assumptions
- State of health is a percent of the original capacity.
- The buffer is a percent of the health-adjusted pack, not of the nameplate.
- No temperature model is applied.
Worked example
A 77 kWh pack at 92% health, with an 8% buffer, has 65.17 kWh usable.
Input definitions
- State of health
- The percent of nameplate capacity the pack still holds.
- Buffer
- The percent of the remaining capacity you do not plan to use.
Limitations
State of health comes from the car or a test, not from this page. The result is not a diagnosis of the battery.
Questions
Why multiply twice?
Health describes wear. The buffer is a choice about how empty you are willing to go. They are different percents.
Where are the miles?
On the EV range page, which starts from usable kilowatt-hours and an efficiency.