State of charge (SoC) estimates how full the battery is right now. State of health (SoH) estimates how much capability a battery retains compared with a reference condition when it was new. A battery can show 100% SoC while having less than 100% SoH.
The simplest comparison
| Question | SoC: state of charge | SoH: state of health |
|---|---|---|
| What does it describe? | Remaining charge relative to the usable charge window | Condition relative to a defined new-battery reference |
| Does it change throughout a trip? | Yes—constantly while driving or charging | Usually gradually; estimated values may also be recalibrated |
| Can it read 100% on an older battery? | Yes | Not necessarily; capacity may have decreased |
| Best use | Trip planning and charging | Battery-aging assessment and used-car evaluation |
What does 100% SoC actually mean?
SoC is the battery’s current charge level, similar to the fuel gauge in a conventional car. The displayed 0–100% is normally managed inside the vehicle’s allowed usable window, not an exact measurement of every cell’s physical capacity. This means 100% SoC does not prove the battery has its original energy-storage capacity. Read our existing state-of-charge definition for SoC estimation and dashboard behavior.
What does 90% SoH mean?
When SoH is defined by retained energy capacity, 90% SoH generally indicates the battery can hold about 90% of its reference energy under comparable measurement conditions. It does not mean there is only 90% charge in the battery today. Some diagnostic systems also consider resistance and power capability, so SoH definitions are not necessarily identical across brands or reporting services.
Illustrative capacity example—not a real vehicle specification
- Reference usable capacity when new: 60 kWh.
- Estimated present usable capacity: 54 kWh.
- Capacity-based SoH: 54 ÷ 60 × 100 = 90%.
- When charged to 100% SoC today, that example pack still holds approximately 54 kWh under comparable conditions.
How is battery health estimated?
The battery management system monitors voltage, current and temperature while software estimates charge and condition. Some methods combine operating history with models, discharge/charge observations, diagnostic testing and cell measurements. Temperature, calibration, test procedure, buffer changes and the definition of usable capacity can influence the reported percentage.
A displayed SoH percentage is therefore an estimate, not a perfect measurement of the car’s future lifespan. Independent tests and manufacturer-certified battery reports may use different methods and assumptions.
Will 90% SoH always mean 10% less driving range?
Not necessarily. Lower available capacity can reduce potential range if consumption stays the same. But real-world range also depends on speed, weather, driving style, tires, software and the heating/cooling system. A car with a lower SoH could outperform another in specific conditions because the vehicles themselves differ.
What contributes to battery aging?
- Calendar aging: degradation can occur while parked, influenced by time, temperature and stored charge level.
- Cycle aging: charge and discharge usage contributes to wear, depending on depth of discharge, power, temperature and chemistry.
- Cell imbalance or thermal differences: pack condition can depend on the weakest portions of the system, not only a fleet-average capacity figure.
Follow your vehicle manufacturer’s storage and charging recommendations; different cell chemistries may have different instructions.
Checking SoH on a used EV
- Ask whether the battery report is manufacturer-certified, independently measured or a simple estimate from a diagnostic application.
- Confirm the exact model, battery pack variant, test conditions and definition of SoH.
- Review battery warranty coverage, exclusions, service history and any prior battery replacements.
- Check usable capacity, charging behavior and possible fault codes with a qualified EV specialist—not merely the dashboard’s current SoC.
Frequently asked questions
Can a battery be fully charged but worn?
Yes. A dashboard 100% charge level refers to the present usable window, not restoration of original battery health.
Does 95% SoH mean I must replace the battery?
No. A health percentage by itself does not determine whether a vehicle requires repair or replacement; use the manufacturer’s diagnostic and warranty criteria.
Continue learning
Technical sources
- Volvo Cars — Battery health and state-of-health certificate
- U.S. DOE AFDC — EV battery basics and life considerations
- Battery University — Battery state of health and state of charge terminology
Vehicle specifications, battery measurements and integration terminology vary by manufacturer, model year and market. Explanatory examples are not verified vehicle specifications.