How BattGrade calculates State of Health
1. Overview
BattGrade issues independent battery health certificates for electric vehicles. This document explains, in plain terms, how a State of Health (SoH) score is produced, from the raw data we read out of a vehicle to the letter grade printed on a certificate. We publish it because trust requires transparency.
2. Data we read
Over a standard OBD2 connection, the BattGrade app reads parameters exposed by the vehicle's Battery Management System (BMS), including per-module voltages, pack and cell temperatures, charge/discharge cycle counts and the manufacturer's reported usable capacity where available.
- Per-module voltage and balance
- Cell and pack temperatures during the read
- Cumulative charge cycles
- Vehicle identity (VIN), make, model and year
3. Normalization
Different manufacturers report capacity and degradation differently. Our normalization layer maps each vehicle's raw readings onto a common reference so that a score means the same thing across a Tesla, a Hyundai and a Renault. The reference models are derived from aggregated, anonymized data across thousands of certified vehicles.
4. Scoring & grades
The normalized result is expressed as State of Health: present usable capacity as a percentage of original. Grades map directly to SoH bands: A is 85–100%, B is 70–84%, and below 70% is graded C or lower. Grades are derived from the score and are never assigned by hand.
5. Independence
BattGrade is a private trust layer, not a government authority. We are not party to any sale. The inspector runs the test, but the score is computed by our engine from objective data and cannot be edited after a certificate is issued.
6. Versioning
Every certificate is stamped with the algorithm version used to produce it. When the methodology changes materially, we publish a new version here and preserve prior versions so any historical certificate can always be interpreted against the rules in force when it was issued.