Battery state-of-health (SoH) is the single most important number for judging a used Tesla. It tells you how much of the original pack capacity is still usable today, and it quietly drives range, resale value, and charging behaviour.
What state-of-health actually measures
SoH compares the pack's present usable capacity against its rated capacity when new. A car that left the factory with 75 kWh and now delivers 70.5 kWh of usable energy sits at roughly 94% SoH. The figure is a ratio, not a fault code — every battery loses some capacity over time.
Why packs degrade
Degradation is normal and mostly gradual. The main drivers are:
- Calendar ageing — chemistry drifts slowly with time, even when parked.
- Cycle count — every full charge-discharge cycle adds a little wear.
- Heat — sustained high temperatures accelerate capacity loss.
- Charging habits — frequent 100% charges and repeated DC fast-charging add stress.
A pack that lost 5% in its first two years has not "failed" — early degradation is faster, then the curve flattens for a long, stable middle life.
Reading the numbers
The maths behind the headline figure is simple:
usable_capacity_kwh = full_pack_kwh * (1 - degradation_pct)
state_of_health = usable_capacity_kwh / rated_capacity_kwh
If you know the rated capacity and the measured usable capacity, you can sanity-check any SoH claim yourself. The report does this for you across the full telemetry history rather than a single snapshot.
Battery health is one of the most important metrics for any electric vehicle. Here is how to read yours.
Key metrics
Battery Level vs. Usable Battery
- Battery Level is what Tesla displays on the dashboard, the percentage shown on your screen
- Usable Battery is the actual amount available for driving, which is slightly lower due to buffer reserves. Tesla reserves a small portion of total capacity to protect the cells from deep discharge, extending overall battery life
State of Health (SoH)
SoH is the single most important number for assessing long-term battery condition. It shows what percentage of the battery's original capacity remains. For example, a 75 kWh battery pack with 95% SoH has roughly 71.25 kWh of usable capacity.
SoH is included in every report.
Battery Capacity (kWh)
The current energy capacity of your battery pack in kilowatt-hours. Compare this against the original factory capacity to understand how much energy your battery can still store.
Range estimates
Tesla provides three different range figures, each calculated differently:
- Rated Range - Based on Tesla's EPA or WLTP rating for your model at the current charge level. This is the "official" number.
- Ideal Range - Estimated range under ideal conditions: moderate speed, flat terrain, comfortable temperature, no heavy loads.
- Estimated Range - A more conservative figure based on your actual recent energy consumption. This is usually the most realistic for daily use.
The gap between rated range and estimated range often widens as the battery ages, since rated range is based on a new battery's performance.
Charge Limit
Your configured maximum charge percentage. Tesla recommends:
- Daily driving: 80-90% to minimize wear on the cells
- Long trips: 100% only when you need the full range
- Storage: 50-60% if the car will sit unused for an extended period
Fast Charger Information
Your report shows whether a DC fast charger is connected and details about it:
- Charger type - Supercharger, CCS, CHAdeMO
- Charger brand - Tesla, Ionity, etc.
- Charging power - Current power delivery in kW
- Voltage and current - Electrical details of the charging session
What affects battery health?
- Age - All lithium-ion batteries degrade over time, even without use, due to chemical aging
- Mileage and charge cycles - Each full charge-discharge cycle causes incremental capacity loss
- Charging habits - Frequent DC fast charging (Supercharging) and regularly charging to 100% accelerate degradation by stressing the cells at high voltage
- Temperature - Extreme heat accelerates chemical degradation; extreme cold temporarily reduces available capacity. Tesla's thermal management system mitigates this but cannot eliminate it entirely
- Usage patterns - Aggressive acceleration and sustained high-speed driving increase thermal stress on the pack
Is my battery healthy?
A small amount of degradation is completely normal and expected.
General guidelines:
- Above 95% SoH - Excellent condition
- 90-95% SoH - Normal for a vehicle with moderate mileage
- 85-90% SoH - Typical for high-mileage or older vehicles
- Below 85% SoH - Worth investigating. Consult a Tesla service center if the degradation seems excessive for your vehicle's age and mileage
Tesla's battery warranty covers significant capacity loss (typically below 70% within the warranty period).
Why do range estimates differ from real-world range?
Several factors cause the displayed range to differ from actual driving range:
- Speed - Highway driving at 120 km/h uses significantly more energy than city driving at 50 km/h
- Weather - Cold weather can reduce range by 20-40% due to battery heating and cabin heating
- Elevation - Climbing hills uses more energy (though descending recovers some via regenerative braking)
- Payload - Extra passengers and cargo increase energy consumption
- HVAC - Air conditioning and heating draw from the battery
- Tire pressure - Under-inflated tires increase rolling resistance and reduce range
What you can control
You cannot stop calendar ageing, but you can slow the rest: keep the daily charge limit around 80%, avoid leaving the car at very high or very low charge in the heat, and reserve DC fast-charging for trips. Healthy habits keep the curve flat — and a flat curve is exactly what a buyer wants to see.