Short answer: A percentage indicating how much of your battery's original capacity remains after use and aging.
Explanation
State of health measures your battery's current maximum capacity compared to when it was new. A brand new EV has 100% SoH. After a few years of use, it might show 95% or 90%, meaning the battery holds slightly less energy than it originally did. This is normal and expected.
You typically will not see SoH on your car's dashboard unless you dig into a diagnostic menu or use a third-party OBD reader. Some manufacturers display it in the car's app or service menu. It matters most when buying a used EV, because a car with 85% SoH has lost 15% of its original range.
Battery degradation happens gradually and depends on factors like temperature exposure, how often you charge to 100%, how often you use DC fast charging, and how many total charge cycles the battery has gone through. Most modern EVs lose about 2-3% of battery health per year under normal use, and manufacturers typically warranty the battery to 70% SoH over 8 years.
Where you'll see this
- On your car dashboard
- In charging network apps
Common confusion
People sometimes confuse SoH with SoC. SoC is your current charge level (like a fuel gauge). SoH is the overall health of your battery over its lifetime (like engine condition). A battery at 90% SoH and 50% SoC has half of 90% of original capacity available.
Example
A 3-year-old Nissan Leaf with 92% SoH and a 40 kWh battery now has an effective capacity of about 36.8 kWh, meaning roughly 8% less range than when new.
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