What is State of Health (SoH)?
State of Health (SoH) explained — what it means, what's a good number, how it affects resale value, and how VoltValue measures it.
What is State of Health (SoH)?
State of Health (SoH) is a percentage that represents your EV battery's current capacity compared to when it was brand new.
- 100% = battery performs exactly as it did when new
- 90% = battery holds 90% of its original capacity (and range)
- 80% = battery holds 80% — the common warranty threshold
It's the single most important number for understanding an EV battery's condition — more reliable than range estimates, which fluctuate based on temperature, speed, and driving style.
Why SoH matters more than range
The range displayed on your dashboard changes constantly — it goes up when you drive slowly, down when it's hot, and varies with tire pressure and air conditioning use.
SoH is different. It measures the underlying capacity of the battery itself, not how far you'll go on a given day. Two cars showing "300 km" of range can have very different SoH numbers — and very different long-term value.
For buyers, dealers, and finance companies, SoH is the number that answers: "Is this battery fundamentally healthy, or has it degraded significantly?"
What's a healthy SoH?
Battery degradation is normal and expected. As a general reference:
| Age | Healthy SoH range |
|---|---|
| 1–2 years | 95–100% |
| 3–4 years | 90–96% |
| 5–6 years | 86–93% |
| 7–8 years | 82–90% |
Most EVs lose roughly 1–3% per year under normal use. Numbers significantly below these ranges for the same age and mileage deserve a closer look.
The 70% warranty threshold
Tesla's battery warranty guarantees that SoH will not drop below 70% within 8 years or 160,000 km (whichever comes first). If it does, Tesla covers a replacement.
This means:
- Above 80%: strong battery, good resale value
- 70–80%: normal wear for older/higher-mileage vehicles
- Below 70%: may qualify for warranty replacement — contact Tesla Service
How does SoH actually degrade?
Battery capacity decreases from two types of aging:
Cycle aging — wear from charging and discharging. Every cycle slightly reduces maximum capacity. This is why charge habits matter.
Calendar aging — degradation over time, even when not in use. A battery stored at 100% charge in a hot environment ages faster than one kept at 50% in a cool garage.
Both types are normal. Good charging habits can slow both significantly.
→ Best charging habits to extend your battery life
How VoltValue measures SoH
VoltValue uses two methods depending on your tier:
Estimated tier: We calculate SoH from your Tesla's range telemetry via the official Tesla Fleet API — using a weighted median across up to 180 days of readings to remove noise from temperature and driving conditions.
Verified tier: We cross-check the range-based estimate against your battery's nominal full-pack capacity from BMS data (Scan My Tesla or TeslaFi), within ±7 pts (NMC) or ±12 pts (LFP). This is the same figure Tesla service technicians use.
→ Full methodology: How we calculate SoH
SoH and resale value
A higher SoH meaningfully affects what a used EV is worth. Buyers and finance companies increasingly ask for independent battery verification before making an offer or approving a loan.
A VoltValue Passport puts your SoH on record — locked at issuance, publicly verifiable, and shareable with anyone.