How much EV battery degradation is normal?

Every lithium-ion battery holds a little less energy as it ages, and an EV's traction battery is no exception. Carmakers say so plainly in their own manuals, and their warranties show where normal wear ends and a fault begins. What varies a lot is how fast it happens, because that depends on the battery's chemistry and cooling, the climate, and how the car is charged and stored.

Is some EV battery degradation normal?

Yes, and carmakers say so in their own manuals. Nissan's Leaf owner's manual says the battery's capacity "will, like all such batteries, decrease with time and usage", and that the resulting drop in range "is normal, expected, and not indicative of any defect" (Nissan Leaf owner's manual). Tesla's Model 3 manual says the battery "naturally degrades over time and with energy use", so the range available on a full charge can gradually fall (Tesla Model 3 manual). Its battery health page says energy retention depends on factors such as age, pack size and chemistry, and how you drive and charge (Tesla battery health).

So a car that shows somewhat less range after a few years is behaving as designed. The question is how much less.

How much degradation do warranties treat as too much?

Most of the US warranties we checked draw the line at 70% of original capacity over 8 to 10 years; Nissan uses the Leaf's capacity gauge instead. A battery capacity warranty is the clearest published line between normal and not. These are the US terms we checked, quoted from each maker's own document:

A few details matter when you read your own:

• The 12-volt battery is separate. Hyundai covers the ordinary 12-volt battery for 3 years or 58,000 km (36,000 mi), not under the EV battery warranty. Our guide to EV 12-volt batteries explains why that one matters too.
• Nissan doesn't give a percentage. The Leaf warranty is based on the gauge. A repair under it "may not return your lithium-ion battery to an 'as new' condition", only to nine segments or more.
• Gradual loss above the threshold is not covered. Nissan says loss from "gradual capacity loss is NOT covered" beyond the terms of its capacity coverage. Hyundai says all lithium-ion batteries lose energy with time and use, and ties its cover to the 70% line. Hyundai's wording ("not to degrade more than 70% of the original battery capacity") is loose; our reading, consistent with its repair clause, is that 70% of original capacity is the floor.
• Terms change by country, model and year. Tesla's page says it is for general knowledge and your vehicle's own warranty is the authority, and its terms apply by purchase date, so the rows above may not match the warranty that came with your car. Canadian and other terms can differ from the US ones above.

The practical reading, which is ours: a battery that is still well above 70% after 8 to 10 years is within what these makers expect. One that is heading for that line early is worth raising with a dealer while the warranty still runs.

How long does an EV battery last?

EV batteries "may last 12 to 15 years in moderate climates and 8 to 12 years in severe climates", according to a DOE study cited by the federal fuel economy site, which the US Department of Energy and EPA run (fueleconomy.gov). That is a broad estimate, not a promise for any one car.

There is no single "normal" percentage per year that holds across makes. Chemistries differ, some packs are liquid cooled and some are not, and climates and charging habits vary widely. Be wary of any one figure presented as universal.

What makes an EV battery degrade faster?

Heat. The makers' advice keeps coming back to temperature. Nissan tells Leaf owners to avoid long exposure to extreme temperatures, to park in cool places out of direct sun, to let the battery cool down before charging, and to avoid sustained high battery temperatures. Tesla says to avoid leaving a Model 3 above 60 °C (140 °F) or below −30 °C (−22 °F) for more than 24 hours at a time.

Laboratory work shows why. Idaho National Laboratory cycled two battery packs from 2012 Nissan Leafs in a 30 °C (86 °F) chamber, twice a day, for 13 months. Those packs have no active cooling. One pack was charged only at Level 2 and the other only by DC fast charging. By the equivalent of about 80,000 km (50,000 mi) of driving, they had lost 23.1% (Level 2) and 28.1% (fast charged) of their capacity, far more than individual cells from the same kind of pack, tested between aluminum plates that limited their temperature rise (INL, Journal of Power Sources). The researchers put part of the difference down to higher and uneven pack temperatures. That was a deliberately harsh test of an early, passively cooled pack, so it is not a forecast for a modern car. It does show that heat matters.

Sitting very full or very empty. Tesla advises avoiding leaving the battery "at or near 0% or 100% for long periods of time". For vehicles with a recommended daily limit of 80%, it says to keep the daily limit at about 80% and save 100% for long trips. For long storage, it says to leave the battery at around 50% and plugged in. Nissan says not to leave a Leaf for more than 14 days with the charge gauge at or near zero.

Frequent fast charging. Nissan recommends normal (Level 1 or Level 2) charging for usual use and says quick charging should be minimized; Tesla says to charge at Level 1 or Level 2 whenever possible and save Supercharging for road trips. What studies have found about how much it matters is in our guide to DC fast charging.

Extreme cold in storage. Nissan says not to store a Leaf below −25 °C (−13 °F) for more than seven days. Cold mostly reduces range and charging speed for the day rather than capacity for good, but storage limits are there for a reason.

How do you check your own EV battery's health?

• Use the car's own health reading, where there is one. On a Model 3, Tesla's manual points to Controls > Service > Battery Health. Some cars also offer a Battery Health Test that needs an AC charger of at least 5 kW for up to 24 hours and discharges the battery low along the way. Tesla recommends running it only if you have a concern about energy retention.
• Read the capacity gauge on a Leaf. It is the 12-segment gauge the warranty refers to.
• Otherwise ask the dealer for a capacity test, especially before a warranty ends or before buying a used EV.
• Don't judge by one range estimate. The number on the dash changes with temperature, recent driving and heating or cooling use. Our advice is to compare like with like: similar season, similar trips.