State of Health (SOH) tells you how much of the original battery capacity remains. Here's how to use it. Reading the report: SOH is usually shown as a percentage of original capacity. A car at 90% SOH retains roughly 90% of its original range. Also check for cell imbalance (voltage spread between modules)—a low SOH with balanced cells is often fine, but high imbalance causes sudden range drops and charging problems. Acceptable thresholds: for a car under 3 years old, expect 90%+ SOH. For 3-5 years, 85-90% is normal. Below 80% SOH, the battery may soon need replacement—replacement costs can exceed the car's value, so negotiate hard or walk away. How to verify: don't trust a screenshot. Ask for a live screen recording of the diagnostic app (like the brand's official tool) starting from the car's VIN page. Cross-check the fast-charging curve: a healthy battery charges at near-peak rate up to 60-70%; a degraded one tapers early. Finally, remember that hot climates degrade batteries faster—if the car spent its life in southern China, scrutinize SOH more carefully.

Mainstream Chinese automakers rarely publish official English versions of their underlying circuit diagrams. We can provide some models' original Chinese technical documents (PDF) for B2B clients, which you will need to translate for your local mechanics using translation software.

For gasoline cars, insist on a compression test: each cylinder should read within 10-15% of the others, and the actual values should match factory specs for that engine. A single low cylinder points to worn rings or valve problems that idle checks will never reveal. A leak-down test goes further. It pressurizes each cylinder and measures how much air escapes and where. Air hissing from the oil filler cap means ring wear; from the intake or exhaust means valve issues; bubbles in the radiator coolant mean a head gasket problem. This is the single most revealing test for engine condition. Also request OBD scan data with freeze-frame records, a coolant system pressure test (to catch hidden leaks), and an inspection of the timing belt or chain condition with service history. For electric vehicles, compression tests don't apply — instead ask for a battery health report from the BMS, motor insulation readings, and a road test logging any inverter or drive-unit fault codes. A written report with photos or video of each test is essential evidence for your records.