Buying a Used EV: What Battery Health Means and How to Check It

With a used petrol car, the big worry is the engine. With a used electric car, it is the battery. The battery is the most expensive single component in an EV. It gradually loses capacity with age and use, and its condition decides how much range you will actually get. The good news is that EV batteries are built to last a long time, and you can check their condition before you buy.

What "battery health" means

Every lithium-ion battery slowly loses capacity, so it holds a bit less energy over time. This is called degradation, and the remaining capacity compared with when the battery was new is often called state of health (SOH). A battery at 90% SOH that originally gave 250 miles of range might now give roughly 225 miles under the same conditions.

The US Department of Energy's Alternative Fuels Data Center (AFDC) explains that EV batteries "have a limited number of charging cycles," which is also called "cycle life." It adds that they are "designed for extended life but will wear out eventually." Degradation is usually gradual, not sudden. Normal capacity loss is different from a fault, such as a failed module, which a warranty is meant to cover.

How long do EV batteries last?

The federal government's estimates are reassuring:

• The AFDC cites predictive modelling by the National Laboratory of the Rockies, a Department of Energy laboratory, which suggests "today's batteries may last 12 to 15 years in moderate climates (8 to 12 years in extreme climates)."
• FuelEconomy.gov cites a DOE study with the same ranges: 12 to 15 years in moderate climates and 8 to 12 in severe ones.

The AFDC lists the factors that affect battery life: climate, "driving and charging patterns, battery cell chemistry and design, and the vehicle-battery-environment thermal system." Cars with active liquid cooling generally manage battery temperature better than those without.

Battery warranties

The AFDC notes that "several manufacturers of electric vehicles are offering 8-year/100,000-mile battery warranties." New Jersey's Department of Environmental Protection, in its used-EV buyer's guide, says most battery coverage runs "eight years or 100,000 miles after the initial purchase, whichever comes first."

Points to check on any specific car:

• Start date. Coverage normally runs from when the car was first sold or put into service, not from when you buy it.
• Transferability. The New Jersey guide warns that "not all warranties are transferable to subsequent owners."
• What is covered. It also cautions that some warranties "may only cover battery failure, but not battery capacity degradation." Where capacity is covered, there is usually a stated threshold below which the manufacturer will repair or replace. Read the warranty booklet for the exact figure.
• Model year differences. Terms "can vary from model year to model year."

If you buy outside the warranty, a replacement battery can be expensive. The AFDC says manufacturers "have not published pricing for replacement batteries," and if one needs replacing outside the warranty, "it may be a significant expense."

How to check a used EV's battery

1. Get a battery health report. The New Jersey guide advises asking "an experienced EV mechanic or dealer to perform an on-board diagnostics check to measure the health of the battery." Some manufacturers and dealers provide official SOH reports. Third-party testing tools exist too.
2. Compare range with the original rating. Charge to 100% if the owner allows it and look at the range estimate. Remember that the estimate depends on recent driving and temperature, so treat it as a rough check.
3. Look at the car's history. Age, mileage and climate all matter. The New Jersey guide notes "continued exposure to extreme temperatures can contribute to EV battery degradation." A car that spent years in a very hot climate deserves extra scrutiny.
4. Check for recalls and service records. The guide says checking open recalls "is a must." Battery-related recalls and any completed module replacements should appear in the service history.
5. Confirm the remaining warranty in writing with the manufacturer or a franchised dealer. Certified pre-owned EVs from franchised dealers may come with extended factory coverage.
6. Ask about connected services. Many EVs rely on a smartphone app for charging control and remote access. The guide notes this "might not be available, or free," on a used car.

Does some degradation matter?

Often less than people fear. The New Jersey guide makes a practical point: "A used EV with some battery degradation could still meet your needs if it maintains adequate range." Work out your real requirements first: daily mileage, how often you take long trips, and whether you can charge at home. A car that has lost 10% of its range may still be a bargain if the remaining range comfortably covers your driving.

Looking after the battery once you own it

The New Jersey guide lists five habits for prolonging battery life:

1. Follow the manufacturer's charging recommendations.
2. Keep the battery between 20% and 80% for daily use.
3. Minimise exposure to heat, for example by parking in the shade.
4. Limit use of DC fast chargers.
5. Don't leave the car fully charged for long periods.

Advice varies by battery chemistry, and some manufacturers give different charging guidance for lithium iron phosphate (LFP) batteries, so your owner’s manual takes priority over general tips.

The short version

Battery health is the main thing to assess on a used EV. Batteries lose capacity gradually. Federal estimates suggest 12 to 15 years of life in moderate climates, and many cars carry an 8-year/100,000-mile battery warranty. Before buying, get a diagnostic health report, check the warranty's start date, transferability and capacity coverage, review recalls and climate history, and make sure the remaining range fits how you drive.

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