EV Battery Calculator

This is a handy app to estimate your effective EV battery size based on how much energy it takes during charging.

This is really a pretty simple calculation, but it might not be initially obvious. The main use for this app would be to track battery degradation. Most, EVs primarily display an anticipated mileage range via the GOM (Guess-O-Meter) display.

When using a DC fast charger to charge your vehicle, the charger communicate with the battery which will report back the state-of-charge (SOC). As energy is delivered the SOC will increase (duh). The actual charge rate can vary based on both the charger’s and the battery’s control.

In the end, after a charging session, a measured about of energy (kWh, kiloWatt-hours) will have been transferred to the battery. The charger will also know and report the change in the SOC from the beginning to the end. So, for example, if the SOC went from 25% to 75% we can assume that the amount of energy supplied was 50% of the total battery capacity. So, if 30 kWh was supplied, we can estimate that the total effective battery size is twice that or 60 kWh.

It is this simple calculation of projecting a total battery size from the charging data that this app performs.

The larger the charge session, the more accurate the size estimation will be. But also, more frequent calculations can be done to see trends over time.