Every EV battery degrades. The lithium-ion cells undergo chemical changes with every charge cycle, every temperature extreme, and every passing month. This is normal and expected. The question is whether the car you're looking at is within the normal range — or accelerating toward an expensive problem.
How Lithium-Ion Batteries Age
Calendar ageing happens from just existing. Chemical reactions slowly reduce capacity regardless of driving. The rate depends on storage temperature and average state of charge.
Cycle ageing happens from charging and discharging. Each cycle causes a tiny irreversible change. The rate depends on cycle depth, charging speed, and temperature during charging.
The Degradation Curve
Year 1: 3–5% loss (steepest, chemistry stabilising)
Years 2–4: 1.5–2.5% per year (curve flattens)
Years 5–7: 1–2% per year (gradual decline)
Years 8–10: 1–1.5% per year (continues to slow)
Five Things That Kill Batteries Faster
1. Heat
The single biggest factor after time. Cells degrade measurably faster above 30°C. Liquid-cooled batteries (Tesla, Hyundai, VW, BMW) degrade 30–50% slower than air-cooled (early Nissan Leaf) because the cooling keeps cells in their optimal range.
2. Frequent Rapid Charging
DC rapid charging (50kW+) generates more heat than home charging (7kW). A car exclusively rapid-charged for 50,000 miles shows 3–8% more degradation than one primarily home-charged. Rapid charging isn't bad — but exclusive rapid charging is measurably harder on the pack.
3. Deep Cycling
Regular 0–100% cycles stress cells at both extremes. Keeping daily use between 20–80% reduces wear by roughly 30% compared to full cycles.
4. Sitting at 100%
Storing at full charge accelerates calendar ageing. Charge to 100% for a trip and drive it down within hours — fine. Charge to 100% every night and sit for 12 hours — measurable cumulative impact over years.
5. Charging When Frozen
Charging a battery below 0°C can cause permanent lithium plating. Most modern EVs have preconditioning to warm the pack first. If yours doesn't, avoid rapid charging in freezing conditions.
How to Measure It Accurately
The dashboard range fluctuates daily — it's for trip planning, not health tracking. The BMS estimate in hidden menus is better but still self-reported and can drift by 3–8%.
An Aviloo certified test measures the battery independently of the car's own systems. Timestamped, QR-verifiable, accepted by dealers and insurers across Europe. £79 through PAD, mobile across South Wales.