EV charging costs and battery health: what to actually expect

Electric vehicle running-cost comparisons often lead with a single headline figure, cost per mile versus a petrol equivalent, that can be accurate for one specific charging pattern and misleading for another. The real answer depends heavily on where the charging happens, which is a bigger variable for EVs than the equivalent question ever was for petrol cars.

Home charging is usually the cheapest option

Charging overnight on a domestic electricity tariff, particularly an off-peak or EV-specific tariff where available, is typically the lowest-cost way to run an EV, often working out to a fraction of the equivalent petrol cost per mile. This is the scenario most favourable headline comparisons are built on, and it holds well for anyone with off-street parking and home charging access.

Public charging narrows or erases the gap

Public fast and rapid charging is priced differently from home electricity and generally carries a premium reflecting the infrastructure cost of high-power charging equipment. Depending on the network, the tariff, and whether the driver holds a subscription with that network, public rapid charging cost per mile can land close to, or in some cases above, petrol cost per mile. This is a meaningful caveat for drivers without home charging access, since their realistic running cost is closer to the public-charging figure than the home-charging one.

Battery health and degradation

Battery degradation, the gradual reduction in usable capacity over the vehicle's life, is a real phenomenon but has generally proven slower in practice than early adopters feared based on consumer electronics battery behaviour. Degradation rate depends on charging habits, climate, and battery chemistry, and manufacturers commonly publish a warranty threshold guaranteeing a minimum percentage of original capacity retained after a stated number of years or miles, which offers a useful, comparable benchmark across models.

What accelerates degradation

• Frequent fast charging to 100 percent, rather than charging to a lower daily-use threshold, is associated with faster capacity loss over time in most battery chemistries.
• Prolonged exposure to extreme heat, particularly when the vehicle is charged or stored at high temperatures, accelerates degradation more than cold exposure typically does.
• Leaving a battery at very high or very low charge for extended periods rather than a moderate range is generally discouraged in manufacturer guidance.

What manufacturer warranties actually promise

Battery warranties typically guarantee against capacity dropping below a specified percentage within a set mileage or time window, rather than promising no degradation at all; reading the specific percentage and window in the warranty document is more informative than relying on general reassurance from marketing material.

A practical checklist for prospective buyers

1. Establish realistic home charging access and cost before comparing headline running-cost figures to a petrol equivalent.
2. If relying substantially on public charging, research local network pricing rather than assuming the home-charging figure applies.
3. Check the manufacturer's specific battery warranty threshold and duration rather than a general claim of long battery life.
4. For used EVs, ask for a battery health or state-of-health report where the manufacturer or a diagnostic tool can provide one.