Battery health is the single most important thing to check when buying a used electric car. Everything else - range, reliability, resale value - flows from it. A car with a strong, healthy battery is a solid purchase. The same car with a degraded pack is a very different proposition.

This guide explains what battery state of health (SoH) means, what percentage to target, how to read it on every major model you are likely to encounter, and what the numbers actually mean for real-world driving. For the full used EV buying checklist, see our guide on how to check a used electric car before you buy.

What is battery state of health?

State of health (SoH) is the percentage of a battery's original capacity that remains usable. A brand-new battery is 100% SoH. After five years of typical use, most EV batteries sit between 82% and 93% - a modest reduction that most drivers would barely notice day-to-day.

The key is that range scales directly with SoH. A Volkswagen ID.3 with a 58kWh battery has a WLTP range of around 260 miles when new. At 85% SoH, usable capacity is roughly 49kWh - and real-world range drops proportionally to around 220 miles in mixed conditions. At 75% SoH, usable capacity falls to 43.5kWh and real-world range drops to around 195 miles. Still usable for most people, but noticeably less than advertised.

Degradation is normal and expected. What matters is whether a given car has degraded more than average for its age and mileage - and whether the SoH is accurately reflected in the asking price.

What SoH percentage should you target?

As a rule of thumb:

• 90% or above: excellent. Minimal range loss, close to new-car experience. Worth paying a small premium.
• 80-89%: good. Some range reduction but still very usable for most drivers. The majority of well-maintained used EVs sit here.
• 75-79%: acceptable, but negotiate hard. Real-world range reduction is noticeable and resale value is lower. Only buy at a meaningful discount.
• Below 75%: approach with caution. Range loss is significant. Check whether a battery warranty claim is possible before committing. Do not pay close-to-market price for a car in this condition.

The exact acceptable threshold depends on the car's original range. A 75% SoH Kia e-Niro (64kWh, 282 miles WLTP) still has more usable range than a 95% SoH Nissan Leaf (24kWh, 124 miles WLTP). Context matters.

How to check battery health by make

Every manufacturer handles SoH reporting differently. Here is how to read it on the models you are most likely to encounter.

Nissan Leaf (all years)

The Leaf is the most important to check carefully because battery degradation has been more variable on this model than most. The 24kWh Leaf (2013-16) in particular suffered notable degradation in hot climates or with heavy rapid charging use.

The quickest check is the battery capacity bar display on the dashboard: 12 bars represents 100%, and each bar represents roughly 6.25kWh. Ten bars or above is the minimum to target. But bars are a coarse measurement - for a precise SoH percentage, use the Leaf Spy app (iOS and Android, free) paired with a cheap Bluetooth OBD2 dongle plugged into the car's diagnostic port. It displays SoH to one decimal place. Ask the seller if you can run it before viewing, or bring a dongle with you.

Nissan's 8-year/100,000-mile battery warranty covers capacity falling below 9 bars (approximately 75% SoH). Confirm whether the car is still within warranty before negotiating.

Volkswagen ID.3 and ID.4

The ID.3 and ID.4 display battery health directly in the car's settings menu. Go to Vehicle > Range and Charging > Battery and the SoH percentage is shown. No third-party tools needed. This transparency is one of the ID range's underappreciated strengths as a used purchase.

Volkswagen's 8-year/160,000km battery warranty covers capacity falling below 70% SoH.

Tesla Model 3 and Model Y

Tesla does not show a direct SoH percentage in the standard UI. The best proxy is to charge to 100% and note the estimated range shown - then compare against the EPA or WLTP figure for that variant when new. A 2019 Model 3 Long Range rated at 348 miles showing 295 miles at full charge has an implied SoH of around 85%.

For a more precise reading, use a third-party app such as Tessie or Stats for Tesla which can pull battery data via the Tesla API with the owner's permission. Tesla's warranty covers capacity falling below 70% SoH (or 60% on the Standard Range).

Hyundai Kona Electric and Ioniq 5

Hyundai displays SoH through the BlueLink connected app and via the car's energy screen. A Hyundai dealer can also run a full battery diagnostic report - worth requesting before purchase, particularly on 2018-20 Kona models subject to the 2021 battery recall.

Kia e-Niro and EV6

Kia's Kia Connect app displays battery health for connected cars. Alternatively, an OBD2 tool running Car Scanner ELM OBD2 will read SoH from most Kia EV models. Kia dealers can also provide a battery condition report.

MG MG4

The MG4 (2022-onwards) displays battery health directly in the infotainment under Vehicle > Battery. As a newer model, most MG4s on the used market are still within their 7-year/150,000km battery warranty.

Renault Zoe

The Zoe's battery health can be retrieved via a Renault dealer diagnostic. Ask for a Z.E. Battery Check report before buying. On pre-2020 Zoes, also confirm whether the battery is owned outright or still subject to a monthly lease - some early cars were sold with a separate battery rental contract that transfers with the vehicle.

What causes faster-than-average degradation?

Battery degradation is accelerated by several factors. Knowing them helps you assess a car's history and predict how it will age going forward.

Frequent rapid charging: DC rapid charging generates more heat than AC home charging and puts greater stress on battery cells. A car that has been rapid-charged exclusively - for example by a driver without home charging - will typically show more degradation than a home-charged equivalent at the same mileage.

Regularly charging to 100%: most EV manufacturers recommend charging to 80% for daily use and only topping to 100% before long journeys. Cars that have been charged to 100% consistently will degrade faster than those kept in the 20-80% window.

Deep discharging: regularly running the battery very low (below 10-15%) also stresses the cells. Check the car's charging habits if the seller is forthcoming - though most buyers will not have this information.

Age and temperature: all lithium-ion batteries degrade over time regardless of use. Cars that have sat in very hot or very cold conditions for extended periods may show more degradation relative to mileage.

None of these factors are visible from a simple test drive. SoH measurement - using the methods above - is the only reliable way to know what you are actually buying.

Using SoH as a negotiating tool

Once you have a SoH reading, use it. Market pricing for used EVs tends to assume reasonable battery health. A car advertised at a fair market price with an 80% SoH is not actually fairly priced - it is overpriced relative to an equivalent car at 90% SoH.

A rough rule: each 5 percentage points of SoH below 90% justifies a price reduction of 500-1,000 pounds on a mid-range used EV, depending on the model and original battery size. A larger battery (64kWh e-Niro) losing 5% SoH has a bigger real-world impact than a smaller battery (40kWh Leaf) losing the same amount.

Bring the SoH data to the negotiation and make your case clearly. Most informed sellers will engage with it. If a seller refuses to acknowledge battery degradation as a pricing factor at all, consider walking away. For full guidance on what else to check, read our complete used EV buying guide. When you are ready to browse specific models, see the best used electric cars under 20,000 pounds.