The UK used EV market has grown faster than buyer confidence. Prices have fallen sharply in the last 18 months — good news for buyers, but only if you don't accidentally buy a car with a dying pack.
The cost of an HV battery replacement on most EVs runs from £4,000 on a small car to well over £12,000 on a larger one. Knowing the battery's real State of Health before you hand over the money isn't optional — it's the difference between a bargain and a disaster.
Seven Checks to Do Before the Aviloo Test
1. Ask How the Car Has Been Charged
Mostly home charging on a 7 kW wallbox? Good sign. Daily rapid charging at motorway services? Less good — especially on older air-cooled packs like early Nissan Leafs.
2. Check the Service History for Battery-Related Work
Any history of high-voltage warnings, module replacements, BMS recalibrations, or pack replacements should be fully documented. A replacement pack isn't automatically bad — but the paperwork needs to add up.
3. Look at the Displayed Range at 100%
Charge the car to 100% and compare displayed range against the original WLTP figure. A 20%+ drop on a car under 4 years old is a red flag. A 10–15% drop on a 5-year-old car is normal.
4. Check the 12V Battery Age
EVs rely on a small 12V battery for ancillaries and to wake the HV system. A failing 12V causes all sorts of electrical gremlins that look like battery faults but aren't. Ask when it was last replaced.
5. Note Any Error Codes or Warning Lights
Even codes that have been cleared leave a trace in the BMS. A professional scan will reveal cleared fault history — sellers who've "reset" the dash before showing the car can't hide this.
6. Look at Charging Behaviour
If possible, watch the car charge. SOC should climb smoothly. Sudden jumps, plateau periods, or an early charge termination before 100% are signs of cell imbalance inside the pack.
7. Check the Onboard Range Data Against Real-World Reports
Sites like Spritmonitor and EV-specific owner forums track real-world consumption for most EV models. If the seller's car is notably below the fleet average for its age, ask why.
What a Manual Inspection Can't Tell You
None of the above checks — not even watching it charge — tells you the battery's actual State of Health percentage. Individual cell voltages can vary significantly within a pack that looks fine externally. The only way to know is a professional measurement.
A car can pass all seven checks above and still have 72% SOH. Conversely, a car that charges a little oddly might test at 91% SOH. Visual and behavioural checks narrow the field — they don't replace measurement.
What PAD Does on a Pre-Purchase Visit
- Aviloo Flash Test: precise SOH percentage from the BMS — independent of the car's self-reporting
- Cell-level voltage check: identifies imbalanced or failing modules before they become expensive
- 12V battery load test: rules out the most common cause of phantom EV fault codes
- Full OBD scan: reads all stored and pending fault codes across every module, including any cleared battery warnings
- Written certificate: emailed to you on site, shareable with any buyer, dealer, or insurer
If You're Selling, the Certificate Pays for Itself
Research shows certified EVs sell for £450–£900 more on average, and sell faster. An Aviloo certificate removes the buyer's biggest objection — they stop negotiating against the unknown and start engaging with a verified number.
PAD covers Pontypridd, all of Rhondda Cynon Taf, Cardiff, Bridgend, and the wider Valleys area. We come to the seller's address, test on site, and issue the certificate digitally before any money changes hands.