Author: Automotive expert specializing in Chinese vehicles, with hands-on experience in diagnostics, maintenance, and real-world operation of ICE, hybrid, and electric models.
avtomir.site Editorial Team
SOH (State of Health) is one of the key indicators of an electric vehicle’s traction battery condition. It shows how much of the battery’s original energy-storage capacity remains compared with when it was new.
In simple terms, SOH reflects how much the battery has worn down. A brand-new EV typically starts close to 100% SOH, and the figure gradually drops as the car is driven and charged over the years.
There’s an important distinction, though: SOH is not the same thing as the battery’s charge level. Charge shows how much energy is available right now; SOH describes the battery’s condition over the long term.
SOH stands for State of Health — essentially a health score for the battery pack.
As a rough guide:
100% SOH — the battery is performing close to new;
95% SOH — a small, expected loss of usable capacity;
90% SOH — the battery has retained about 90% of its original capacity;
80% SOH — noticeable degradation;
70% or below — worth a closer diagnostic look.
For example, if a new EV has a battery rated at 60 kWh, and after several years of use the actual usable capacity drops to around 54 kWh, the SOH would sit at roughly 90%. The exact calculation depends on the manufacturer’s methodology and the diagnostic system used to measure it.
SOH and Charge Level Are Not the Same Thing
These two figures get mixed up constantly. Picture an EV with a battery at 90% SOH. If the dashboard shows 100% charge, that just means the battery is charged to the maximum level the system currently allows — not the same 100% of capacity the car had when new.
State
New Battery
After Degradation
Rated capacity
60 kWh
60 kWh
Actual usable capacity
60 kWh
54 kWh
SOH
100%
~90%
Dashboard charge after a full charge
100%
100%
So a “100% charged” reading on the dashboard doesn’t mean the battery has retained 100% of its original capacity.
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Every charge-discharge cycle gradually affects the chemical processes inside the cells. A “cycle” doesn’t have to mean a single 0–100% charge — draining from 50% to 100% and then repeating that once more adds up to one full equivalent cycle.
2. High Temperatures
Prolonged exposure to heat can speed up unwanted chemical reactions inside the cells. This is especially relevant for EVs regularly driven in hot climates, under heavy load, or with frequent fast charging. Modern EVs use active thermal management systems for the battery, so the real-world impact of heat varies a lot depending on how a given model is engineered.
3. Very Low Temperatures
Cold weather increases the cells’ internal resistance, temporarily reducing available power and charging speed. It’s important to distinguish between a temporary dip in performance in cold weather and permanent degradation: a shorter winter range doesn’t automatically mean SOH has dropped — much of that performance returns once the battery warms up.
4. Frequent Fast Charging
High-power DC fast charging doesn’t automatically mean a battery will fail sooner. Modern EVs actively manage temperature, current, and voltage, and charging power typically throttles based on the battery’s condition. That said, regular high-power charging does put more thermal and electrical stress on the pack than typical AC charging.
According to a large-scale study by telematics company Geotab, which analyzed more than 22,700 EVs across 21 models, average battery degradation now runs at about 2.3% per year. Vehicles that rely heavily on DC fast charging above 100 kW degrade roughly twice as fast (around 3% per year) as those charged mainly on AC or lower-power DC (around 1.5% per year). Climate turned out to have a much smaller effect on degradation than charging behavior.
Leaving a battery sitting near its upper or lower charge limit for extended periods can also accelerate aging. That’s why automakers typically publish guidance on storage and charge levels — it’s best to avoid leaving a car parked for long stretches fully drained, fully charged, or in high heat.
What Counts as a “Normal” SOH?
There’s no single number that qualifies as normal across every EV. SOH depends on battery chemistry, the cell manufacturer, the vehicle’s age and mileage, cycle count, temperature exposure, charging habits, and the specific algorithm the battery management system (BMS) uses to calculate it.
Still, this rough scale is a useful starting point:
SOH
General Assessment
95–100%
Very good condition
90–95%
Good condition
85–90%
Normal expected wear
80–85%
Noticeable degradation
70–80%
Significant capacity loss
Below 70%
Worth a closer diagnostic check
This table isn’t a universal diagnostic standard — for any specific vehicle, the manufacturer’s own guidance and measurement method matter more than a generic scale.
Why 80% Is Often Treated as a Key Threshold
The auto industry commonly uses roughly 80% of original capacity as a reference point for “significant” degradation — it’s also the threshold that shows up most often in automakers’ battery warranty terms over a set number of years or miles. But crossing that line doesn’t mean the battery suddenly stops working: degradation is a gradual slope, not an on/off switch, and the car keeps running normally with somewhat less range.
How to Check an EV’s SOH
The simplest option is checking the figure directly in the car’s own menu, if the manufacturer exposes it. Many EVs don’t display SOH to the driver at all, though, which is where diagnostic tools come in.
OBD Diagnostics
On many models, a diagnostic port scanner paired with the right app can pull SOH, individual cell voltages, battery temperature, state of charge, usable capacity, cycle count, and BMS fault codes. One catch: this data needs to be read correctly, since different manufacturers use different parameters and calculation methods, and readings can shift with temperature and recent charge history.
Can You Estimate SOH From Range Alone?
Only roughly. If a car was rated for 500 km new and now shows 450 km, that doesn’t automatically translate to a 90% SOH — range is also shaped by temperature, speed, driving style, terrain, tire pressure, climate-control use, wind, cargo load, and the selected drive mode. A meaningful range comparison only works under closely matched conditions.
Why Two Identical EVs Can Have Different SOH
Even two examples of the same model and model year can end up with noticeably different SOH. One car might have spent most of its life on the highway, charged frequently via DC fast chargers, operated in a hot climate, or sat parked at a high charge level for long periods. Another might have charged mostly on AC power, run in a moderate climate, and rarely dropped to a low charge level. That’s why age and mileage alone can’t reliably predict battery condition.
SOH and Cell Balance
SOH isn’t the only number worth checking. Another key metric is the voltage spread between individual cells or cell groups — if one group deviates significantly from the rest, it can point to imbalance, a weak cell or module, a measurement issue, or a temperature-related problem. That’s why, when buying a used EV, it’s worth looking at the full picture rather than relying on a single SOH figure.
Why SOH Can Shift Unexpectedly
Sometimes an owner notices SOH was, say, 94% and then reads 91% after a batch of trips. That doesn’t necessarily mean the battery physically lost 3% of its capacity overnight — SOH is a calculated BMS estimate, not a direct measurement of the energy stored in every cell. The battery management system can revise its estimate after charge/discharge cycles, cell balancing, temperature swings, new measurement data, or a software update. Small shifts in the reading don’t automatically signal sudden battery deterioration.
How to Extend Battery Life
Degradation can’t be stopped entirely, but usage habits can be optimized:
Avoid prolonged battery overheating.
Don’t leave the car sitting fully charged for extended periods without reason.
Don’t store the EV for long stretches at a near-zero charge.
Use fast charging when it’s actually needed, not as a default habit.
Follow the manufacturer’s recommended charge-level range.
Don’t judge battery condition by range alone.
Run a full battery diagnostic before buying a used EV.
Following the vehicle manufacturer’s own guidance matters most here — the optimal charge range can vary by battery chemistry and by model.
What If SOH Is Already at 85%?
That’s not, by itself, a reason to replace the battery. A car with around 85% SOH can keep running normally. The real question is whether the owner is happy with the remaining capacity and range — losing 15% of original capacity might mean a shorter maximum range, more frequent charging, and less buffer on longer drives, but the battery itself can remain fully functional.
What a Low SOH Means When Buying a Used EV
A single SOH reading shouldn’t be evaluated in isolation when shopping for a used EV. Say a diagnostic tool shows 82% — that’s a reason to dig deeper, not an automatic dealbreaker. Worth checking: actual usable capacity, cell voltage spread, BMS fault codes, battery temperature, charging history (if available), mileage, age, the manufacturer’s warranty terms, and real-world range. It also helps to compare the numbers against other examples of the same make, model, and roughly the same age.
The Bottom Line on SOH
SOH reflects how much of a battery’s original capacity and performance remains. As a rough guide: 100% is essentially new, 90% is moderate wear, 80% is noticeable degradation, and 70% is a significant capacity loss. But these numbers shouldn’t be treated as a universal technical standard for every EV — a proper diagnostic looks at SOH alongside actual usable capacity, cell balance, temperature, BMS fault codes, and usage history.
And above all, don’t confuse SOH with charge level. 100% charge means the battery is currently full relative to whatever range it has available. 100% SOH means its calculated condition is close to that of a new battery. For an EV owner, how SOH trends over time usually matters more than any single reading — a gradual, steady decline without sharp drops is exactly what normal battery aging looks like.
Frequently Asked Questions About EV Battery SOH
SOH (State of Health) is a calculated figure showing how much of a traction battery’s original capacity remains compared with when it was new. A new EV typically starts near 100% SOH, and the number gradually declines with use.
Charge (State of Charge) shows how much energy is available right now, and it changes every time you charge or drive. SOH describes the battery’s overall long-term condition and only shifts slowly as the battery ages.
There’s no universal norm, but as a rough guide, 90–100% SOH is considered good condition, 80–90% is typical expected wear, and anything below 80% is worth a closer diagnostic look. The right benchmark depends on the vehicle’s age, mileage, and the manufacturer’s own guidance.
Only roughly. Range is affected by temperature, driving style, terrain, tire pressure, and other factors, so an accurate SOH reading requires an on-board or OBD diagnostic rather than a one-off comparison of range on a single charge.
No, an SOH of around 85% doesn’t by itself mean the battery needs replacing. At that level the pack usually keeps working normally, just with somewhat less range. Replacement typically becomes a real question at much lower SOH values or when diagnostics reveal an actual fault.
