EV battery health: what matters and what doesn't
EV batteries are lasting longer than early critics predicted. Most of the capacity a pack loses comes from time, temperature and how long it sits very full or very empty — not from the occasional road-trip fast charge.
Two kinds of ageing
Calendar ageing happens even when the car is parked. It accelerates with heat and with long periods at a high state of charge. Cycle ageing comes from charging and discharging; deep cycles and high current at extreme temperatures accelerate it. Battery management systems are designed around both.
How much does DC fast charging matter?
Fast charging creates more heat and stress than slow charging, but the car's thermal management and charging curve are built to limit that stress. Large datasets from connected EVs have found only small differences in capacity between cars that fast charge often and those that rarely do. The sensible approach: use fast charging when you need it, and use home or workplace Level 2 charging for daily driving because it is cheaper and convenient.
Cold weather
Cold slows the chemistry. Expect lower range — real-world data shows roughly a fifth less at around freezing, more in deep cold or with heavy cabin heating — and much slower DC charging if the pack is not warmed. Heat pumps and preconditioning while plugged in reduce both effects. Our fast-charge calculator includes a cold-battery setting.
Six habits that help
- For daily use, set a charge limit around 70–90% unless your manufacturer recommends 100% (some LFP-pack cars do).
- Avoid leaving the car at 100% or near 0% for days.
- Park in shade or a garage in very hot climates.
- Precondition before fast charging in cold weather.
- Keep software updated — charging strategies improve over time.
- Do not obsess: convenience and safety beat squeezing out an extra percent of capacity.
Buying a used EV
Ask for a battery health report (state of health) from a dealer, the manufacturer's app or an independent service; compare the car's full-charge range with its original rating in similar weather; and check whether the battery warranty — often 8 years with a capacity threshold — is still in force and transferable.