Anyone buying and selling EVs for stock quickly learns that the battery is the deal. Get it right and margins are solid. Get it wrong and you are sitting on a five figure liability. Knowing how to assess battery health on used electric cars properly is now a core trade skill, just like reading compression figures used to be.
Why battery health matters more than mileage
With combustion cars, mileage is the shorthand for overall wear. With EVs, the traction battery deserves its own separate analysis. Two identical cars with the same mileage can have wildly different state of health depending on charging habits, climate and usage profile.
For trade buyers, battery condition affects:
- What you can safely bid at auction or on a doorstep
- How confident you can be with retail warranties
- Stock turn speed, especially on older high mileage EVs
- Future part exchange risk when that same EV comes back
Ignoring the battery is effectively guessing at the biggest cost item on the car.
Using state of health tools to assess EV batteries
The most reliable way to assess battery health on used electric cars is to read state of health data directly from the vehicle. Most modern EVs store this in the battery management system and expose it through the OBD port, a manufacturer diagnostic tool or both.
Independent tools and apps paired with a quality OBD dongle can give you:
- State of health (SoH) as a percentage of original capacity
- Usable capacity in kWh
- DC and AC charge counts and totals
- Cell voltage spread and temperature data
For trade work, look for tools that log and export data so you can keep a record with the stock file. Consistency matters: use the same hardware and process on every EV so your SoH figures are comparable across cars and over time.
Reading manufacturer battery data correctly
Many brands now show some form of battery data in the infotainment system or service menu. It is useful, but you need to understand what you are actually looking at:
- Some show total capacity, others show usable capacity only
- Some round aggressively, so a 91.6 percent pack appears as 90 percent
- Some reset after software updates or module changes
Always cross check the on screen figure with your independent SoH tool and the vehicle history. A pack that suddenly jumps from 82 percent to 95 percent between services probably had a software update or a module swap. That is not necessarily bad news, but it changes how you price and explain the car.
Typical battery degradation patterns by brand
Every EV degrades, but not at the same rate. Broadly, you will see:
- Early air cooled packs: faster initial drop, then a slower tail
- Modern liquid cooled packs: gentle decline if charging habits are sensible
- High performance models: a bit more wear where drivers lean on rapid charging and full throttle often
Look for patterns in your own stock. Track SoH against age, mileage and usage. Within a year you will know what is normal for each brand and which models you want to avoid at certain mileages. Manufacturer warranty terms also give you a clue: if a brand is happy to back a pack for eight years to 70 percent, they are confident typical cars will sit above that line.
How to price battery risk into trade bids
Once you can read the data, the next step is turning it into numbers on a bid sheet. A simple framework keeps you out of trouble:
- Start with your usual book figure for a clean, average example
- Apply a battery adjustment based on SoH banding
- Layer on any warranty cover that remains on the high voltage pack
- Factor in your local retail demand for older EVs
For example, you may decide that:
Assess battery health on used electric cars FAQs
What is a good state of health percentage for a used EV battery?
For most mainstream EVs, anything above 90 percent state of health is typically considered very strong for a used example and should not need a price hit beyond normal trade negotiation. Between about 80 and 90 percent is common on older or higher mileage cars and can still be perfectly usable, but you should reflect the reduced range in your bid. Once a pack drops into the 70s, you need to buy cautiously, check remaining battery warranty, and be clear with retail customers about expected range.
Can I assess battery health on used electric cars without specialist tools?
You can get a rough feel for battery condition from range tests, dash readouts and service history, but it is not enough for confident trade buying. To assess battery health on used electric cars properly, you really need to read state of health data from the battery management system using a suitable diagnostic tool or app. The cost of basic kit is low compared with the potential loss on a single misjudged EV purchase.
How much should battery degradation affect my trade bid price?
The impact on your bid should reflect both the loss of usable range and the potential cost of future repair. Many traders work with simple bands, applying no adjustment for high SoH packs, a modest deduction for mid 80s figures, and a much stronger deduction or a walk away decision once the battery drops into the low 70s or worse. Local demand, remaining manufacturer battery warranty and the price of replacement or repair options in your area should all feed into your numbers.