Used electric Mercedes models are now a common sight on forecourts, and with the early EQA, EQB and EQC cars coming off finance, there are some tempting prices about. But buying a used EV calls for a slightly different checklist from a petrol or diesel. On an electric Mercedes, the single most important component is the high-voltage battery, and its condition isn’t something you can judge by looking at the car or reading the odometer.
Battery state of health: the number that matters
Every lithium-ion battery gradually loses some capacity over time. The measure of how much it retains compared with new is called its state of health (SoH). A car showing 95% SoH has lost very little; one at 80% will deliver noticeably less range than it did when new.
The range estimate on the dashboard is not a reliable guide to battery health. It’s based on recent driving, temperature and climate control use, so it can look worse in winter or better after a gentle run. The accurate way to read SoH is through the car’s battery management system with Mercedes diagnostic equipment.
What affects battery health on a used EQ?
- Age and mileage: both play a part, though age often matters as much as miles.
- Charging habits: a car that’s been rapid-charged heavily, or regularly charged to 100% and left sitting, may show more degradation than one charged mostly at home.
- Climate and storage: long periods at very high or very low charge aren’t ideal.
- Software: battery management updates can affect how the battery is used and reported.
Check the battery warranty
Mercedes-Benz covers the high-voltage battery on its EQ models with a separate, longer warranty than the rest of the car, typically running for eight years subject to a mileage limit and a minimum capacity threshold. Check the exact terms for the car you’re considering, confirm the original registration date, and make sure the warranty transfers to you. A car that’s a year away from the end of its battery cover deserves a closer look than one with five years left.
Don’t forget the 12V battery
It surprises many owners, but electric Mercedes models still have a conventional 12V battery that powers the car’s control units, locks and systems before the high-voltage system wakes up. When it weakens, the car can refuse to start or throw up a cascade of warning messages, even with a fully charged main battery. It’s one of the most common faults we see on EVs and hybrids, for much the same reasons we covered in why Mercedes batteries fail more often than owners expect.
Other things to check on a used electric Mercedes
- Charging: test both AC (home or wallbox) and, if possible, DC rapid charging. Check the charging port and flap for damage or corrosion.
- Charging cables: make sure the cables that should come with the car are present.
- Brakes: regenerative braking means the friction brakes are used less, so discs can corrode. That’s especially relevant near the coast, as we explain in our post on Wirral’s coastal roads and corrosion.
- Tyres: EVs are heavy and deliver instant torque, so tyres can wear faster than owners expect.
- Service history: EVs still need servicing, including brake fluid, cabin filters and coolant for the battery cooling system. See our guide to hybrid and EQ maintenance.
- Software and recalls: run a recall check and ask whether software updates have been applied.
A pre-purchase inspection is worth it
A used EV can look perfect and drive beautifully on a short test drive while hiding a battery that’s further degraded than the price suggests. A pre-purchase inspection with proper diagnostics takes the guesswork out of it and gives you something concrete to negotiate with.
Thinking of buying a used EQ on the Wirral? Call MB Wirral on 0151 632 0006 to arrange a pre-purchase check before you commit.
