How to Check an EV Battery's Health Before You Buy

Battery health is one of the most important things to check when buying a used electric car, and the good news is that it is more accessible to check than many people assume. The battery's state of health (SoH) tells you what percentage of its original capacity remains, which directly affects how far you can travel on a full charge. A car with a well-maintained battery will behave much closer to its WLTP-rated range than one that has been mistreated or heavily rapid-charged. Before you hand over any money, use the steps below to get a clear picture of what you are actually buying, and visit our Guides index for more used EV buying advice.

What does state of health actually mean?

State of health is a measure of how much usable capacity an EV battery retains compared to when it was new. A battery at 100% SoH has its full original capacity; one at 85% SoH holds roughly 85% of that original energy, meaning proportionally shorter range. Degradation is normal and expected over time and mileage. The rate at which it degrades depends on charging habits, temperature exposure, and how often the car was rapid-charged. Understanding SoH gives you a realistic expectation of the range you will actually get, not just the figure quoted in the brochure.

How can you check battery health yourself?

The easiest first step is the car's own system. Many modern EVs display a battery health or battery status reading in their infotainment screen or companion app. Some manufacturers provide this clearly; others are less forthcoming. If the car has an OBD-II port, you can connect an inexpensive Bluetooth OBD adapter and use compatible software to read the SoH directly. Apps designed for specific brands are widely available and can pull detailed battery data in minutes. This gives you a hard number to work with rather than relying on the seller's word.

What SoH should you look for?

There is no single pass or fail threshold that applies to every car and every buyer. What matters is whether the figure is in line with the car's age and mileage. A car a few years old with high mileage will naturally sit lower than a low-mileage example from the same year. The key question is whether the degradation is gradual and steady (normal) or surprisingly steep for the mileage (a warning sign). Consider what range the car will deliver at the SoH you see, and decide whether that meets your real-world needs. If the reading is unavailable or the seller refuses access, treat that as a red flag.

Is a professional pre-purchase inspection worth it?

For a private purchase, yes. An independent EV specialist can give you a full battery health report alongside the standard mechanical checks. Authorised dealers for most major brands can also run a certified battery health check, often at no charge if you are seriously considering a purchase. This is particularly valuable if you are buying a car where the battery represents a large share of the vehicle's value. The inspection cost is small relative to the peace of mind, and a clean report can also help with your negotiation position.

How does the battery warranty affect things?

Most EV manufacturers offer a separate battery warranty, typically covering the battery for a number of years or a mileage limit, whichever comes first. Many policies guarantee the battery will not fall below a certain SoH threshold during the warranty period, so if it does, the manufacturer must repair or replace it. When buying used, check how much of this warranty remains and whether it is transferable to a new owner. Remaining battery warranty is one of the most valuable things a used EV can have. Check the manufacturer's website for current terms, as these vary by brand and model.

What else should you check alongside battery health?

Battery health is the headline figure, but it is not the only thing. Also check:

• Charging history: frequent rapid charging, especially to 100%, can accelerate degradation more than a moderate charging routine.
• Whether the car supports scheduled charging and has had it used, which suggests a careful previous owner.
• Software updates: an EV kept up to date with manufacturer updates may have received battery management improvements.
• Physical condition of the charging port and any cables included with the car.
• MOT and service history, though EV servicing is simpler than on a petrol car.

Frequently asked questions

Can I check battery health without any tools?

Some manufacturers display a battery health indicator in the car's infotainment screen or companion app, with no additional tools needed. If the car does not show this natively, you will need an OBD adapter or a professional check. Charging the car to 100% and reading the displayed range is a rough guide, but it is not a substitute for an actual SoH reading, as range estimates can be optimistic.

Does mileage tell me how degraded the battery is?

Mileage is useful but not the whole story. Two cars with the same mileage can have quite different battery health depending on how they were used and charged. A car driven mostly on motorways with lots of rapid charging may have degraded faster than one used gently on short trips with home charging. Always get a SoH reading alongside mileage rather than relying on one figure alone.

Is battery replacement expensive on a used EV?

Battery replacement is a significant cost if it falls outside warranty. Costs vary considerably by brand and battery size. When buying used, check the remaining battery warranty and its terms. If the battery is out of warranty and SoH is low, factor a potential future replacement into your budget or negotiate the price accordingly. Check with the manufacturer or a specialist for current pricing.

What is a good SoH percentage for a used EV?

This depends on the car's age and mileage. A relatively new, low-mileage car should be close to its original capacity. An older, high-mileage car will naturally sit lower. Rather than chasing a specific number, assess whether the SoH is consistent with the car's history and whether the resulting real-world range meets your needs.

Do all EVs have the same OBD port for battery checks?

Most EVs have an OBD-II port, but not all expose battery data through it in the same way. Some manufacturers use proprietary protocols requiring brand-specific adapters or software. Check online communities for your specific make before buying an OBD adapter, as users share which tools and apps work best for each model. Independent EV specialists will have the right equipment for most popular models.

Does rapid charging always damage the battery?

Occasional rapid charging is generally well tolerated by modern EV batteries. The concern arises with very frequent rapid charging, especially to 100%, sustained over a long period. Most manufacturers recommend keeping regular charging to around 80% for daily use and reserving full charges for long journeys. A car that was rapid-charged daily to full throughout its life may show more degradation than one home-charged slowly overnight.

Checking battery health before buying a used EV takes only a little preparation but can save you from a costly surprise. If you are new to EVs and unsure which cable or charger you will need for your next car, use our home page reg checker to find the right option, or browse our full charging cables by car guide to get set up from day one.