How to Check EV Battery Health: What SOH Can Tell You?
What does an EV battery health percentage actually tell you? Understand SOH, how it differs from charge level, and the difference between reading the BMS and measuring usable energy. Learn which test to request, what a report should explain, and why one reassuring number cannot answer every battery concern.
By TruWheelz
1 November 2026 · 3 min read
Someone hands you a diagnostic printout showing 92% battery health. Should you feel reassured? Usually, you will want a little more information first. To check EV battery health, start by finding out what the reported SOH represents, then look at the supporting observations and test conditions. If you need to know how much usable energy remains, ask whether that was actually measured. That distinction matters whether you are buying a used EV or trying to understand your own car.
SOC tells you how full it is; SOH describes condition
State of Charge, or SOC, is the charge percentage you see during everyday use. It falls while driving and rises while charging. State of Health, or SOH, compares a battery characteristic with a reference condition. In owner-facing reports, it often concerns remaining capacity or energy. Those definitions need to be stated: capacity measured in ampere-hours and energy measured in kilowatt-hours are different quantities. So a full charge and a high health reading answer different questions. Neither, by itself, is a complete diagnostic assessment.
What does 90% battery health mean?
Suppose a hypothetical battery delivered 40 kWh of usable energy when new and delivers 36 kWh in a comparable test today: 36 ÷ 40 × 100 = 90% energy retention. The comparison works because both values refer to usable energy under comparable conditions. Using an advertised gross pack figure as the baseline could change the answer incorrectly. A report should identify the reference and measurement conditions. This calculation does not tell you how many years the battery has left, or promise a particular range on tomorrow's drive.
| Your question | What to ask the provider |
|---|---|
| What does the car currently report? | Can you retrieve and identify its BMS-reported SOH? |
| Why does it show a warning or behave unusually? | Can you investigate that symptom and capture relevant faults and live data? |
| How much usable energy remains? | Do you perform a defined energy or capacity test, and what does it measure? |
| Has the condition changed since last time? | Can you compare results obtained with a consistent method? |
Equipment support varies by vehicle and battery version. Confirm access before booking rather than assuming every OBD reader can retrieve the same information.
What a diagnostic scan can contribute
A compatible scan may provide the vehicle's own SOH estimate, faults and relevant operating measurements. Ask the provider to separate what the BMS reported from anything the provider calculated independently. Observations at rest, during driving or during charging may help investigate a complaint when those activities are appropriate and included. Record the conditions alongside the numbers; otherwise a later comparison becomes difficult.
What a measured test adds
A defined capacity or usable-energy test records performance across specified boundaries. Ask about the measurement source, starting and finishing conditions, reference and uncertainty. Be careful with charging receipts. Energy supplied at an AC charger and energy delivered by the battery are different measurement points. NITI Aayog's charging guidance explains that an AC supply goes through the vehicle's onboard charger for conversion to DC. A charging receipt therefore does not directly measure battery output. Dividing a charging receipt by a percentage change does not automatically produce a dependable battery-capacity result.
A reassuring SOH does not explain every warning
Capacity is one part of battery condition. NREL research notes that capacity and resistance measurements do not capture all degradation mechanisms. If the car has abrupt charge-percentage drops, interrupted charging or a warning, describe that concern clearly. Ask whether the test investigated it, even if the health figure looks good.
What counts as a good SOH?
There is no single percentage that answers every buyer's or owner's question. Ask how the result compares with a valid reference, what else was found and whether the car meets your needs. Warranty eligibility is a separate question governed by the applicable terms. Do not treat a general internet threshold as approval for a claim or a reason to replace a pack.