If you are researching used electric vehicles, you will encounter the term State of Health SoH repeatedly. It is the single most important number for assessing any used EV battery.
Here is exactly what it means and how to use it.
What State of Health means
SoH is a percentage representing how much of the battery's original capacity remains. A new battery is 100%.
As the battery ages and is used, capacity gradually reduces. 85% SoH means 85% of original capacity remains. The car will deliver roughly 85% of its original range under equivalent conditions.
Degradation is a normal, expected characteristic of all lithium-ion batteries in phones, laptops, and electric vehicles alike. It is not a defect. It is predictable, gradual, and manageable.
The question is not whether degradation has occurred on any used vehicle it will have but how much, and whether that suits the price and the buyer's needs.
What the numbers mean in practice
85% and above: a healthy used battery. Degradation is moderate, range loss is noticeable but not dramatic, and further deterioration over a normal ownership period will be gradual.
75–84%: meaningful range reduction but acceptable on an older or more affordable vehicle if the price reflects it. A vehicle at 80% SoH is delivering 80% of its original range, test that figure against your real daily requirements.
Below 75%: significant capacity loss. The purchase price should reflect this clearly. For context, this is the level at which many battery lease agreements would trigger a free replacement which indicates how the industry itself views this threshold.
Below 60%: over a third of original capacity lost. Only worth considering at a very substantial discount for a buyer with limited daily range needs.
How SoH affects real-world range
Take the original WLTP range figure for the model, this is the lab-test range published by the manufacturer for a new vehicle.
Multiply it by the SoH percentage. That gives you the approximate WLTP equivalent range at the current battery health. Then apply the standard real-world adjustment, typically 75–85% of WLTP in normal UK conditions to arrive at a realistic everyday range figure.
Example: a vehicle with an original WLTP range of 200 miles at 82% SoH has an effective capacity-adjusted range of around 164 miles under test conditions. In real-world UK driving, expect roughly 125–140 miles depending on conditions, speed, and weather.
What to do with the figure
Assess it against your daily driving needs not your occasional long journeys, but your typical day.
A vehicle at 82% SoH is not a problem for a driver whose daily use is under 80 miles and who has access to overnight home charging. It may be a problem for a driver who needs 150 miles of daily range without an opportunity to charge.
Use it as a negotiating point. A battery below 85% SoH is a legitimate basis for negotiating the purchase price downward from the asking figure, even if the vehicle is otherwise excellent.
