On a used gasoline car, mileage and service history tell most of the story. On a used EV, battery health is at least as important — and it is far easier for a seller to obscure than most buyers realize. Here is what to actually check.

What "Battery Health" Actually Means

Battery health, usually expressed as a state-of-health (SoH) percentage, compares a battery's current usable capacity against its original capacity when new. A pack at 92% SoH can still hold 92% of the range it delivered on day one. This figure is read directly from the vehicle's battery management system (BMS) using a diagnostic tool — it is not something that can be reliably estimated by driving the car around the block, which is exactly why sellers who skip this step should raise a flag.

What Actually Degrades a Battery

  • Fast-charging frequency — frequent DC fast-charging generates more heat cycling than slower home charging, and accelerates wear over time.
  • Total mileage and age — both correlate with cycle count, though not as strongly as many buyers assume.
  • Climate exposure — extended exposure to extreme heat is generally harder on a pack than cold, though both matter.
  • Chemistry — LFP packs, including BYD's Blade Battery, degrade more slowly and more predictably than many NMC packs, which is one reason used BYD units tend to hold value well. See our Blade Battery explainer for the technical background.

What a Trustworthy Condition Report Includes

Before agreeing on a price for any used EV, insist on documentation covering:

  • Battery state-of-health percentage from a BMS diagnostic reading, not a verbal claim.
  • Odometer mileage, cross-checked against service or ownership records where available.
  • Number of previous owners.
  • Any accident or major repair history.
  • Current availability status — confirm the unit is actually ready to ship, not pending a separate sale.

Every listing on our used vehicles page publishes all of this up front, precisely because we expect buyers to ask. If a seller cannot produce a battery-health reading on request, treat that as a pricing risk, not a minor omission — it is the single largest variable in what the vehicle is actually worth.