Offered by your dealer
Your EV battery, checked in minutes
The ClearWatt EV Flash Test gives you an independent view of your battery’s health. Your dealer connects to your car for a few minutes, then ClearWatt combines those readings with real-world data on how similar batteries perform and turns it all into a clear EV Flash Report.
No driving, no charging, and most cars are done in under three minutes.
Your Battery Scorecard
Your report grades the battery in four areas, each drawing on a different source of evidence. Together they produce one overall grade.
Battery Condition Indicator
Key on-vehicle indicators
Read from the car itself, including estimated capacity and battery calibration.
Battery Build & Longevity
Key battery attributes
How the battery is designed and built to last, such as its chemistry and pack design.
Relative Condition
Comparative tested vehicles
How your battery compares with similar cars ClearWatt has tested.
Reliability & Ongoing Support
Vehicle maintenance metrics
Signals from how the car is maintained and supported over time.
One overall grade
What each grade means
Excellent
No action neededYour battery scored highly across everything we check. Nothing needs doing.
Good
No warning signsYour battery scored lower in one or more areas, such as capacity kept or how the pack is built for long life.
Investigate
Needs a closer lookSomething needs a closer look, and it is not a fail. Often the cells just need balancing with a slow charge to 100% and a retest. If capacity has dropped below the warranty level while cover is still running, the report says so.
How the test works
The test is more than a single reading from the car. ClearWatt brings together evidence from several sources to grade your battery, and most cars are scanned in under three minutes.
- Step 1
Connect
Your dealer plugs a small reader into the car’s diagnostic port, the same socket used when your car is serviced.
- Step 2
Read and combine
With the car parked and switched on, the reader collects data from the system that manages the battery. ClearWatt combines it with the battery’s design, similar cars it has tested and the car’s maintenance record.
- Step 3
Report
ClearWatt turns it all into your EV Flash Report and sends it to your dealer, who shares it with you.
What else your report shows
Behind the grade, your EV Flash Report sets out the detail in plain language. Depending on your vehicle, it covers:
Estimated capacity
How much of its original capacity the car reports the battery can still hold, shown as a percentage.
Battery calibration
Whether the cells across the pack are Well-balanced or Unbalanced. Healthy batteries keep their cells closely matched.
Charging
Where the charging port is, which chargers suit your car, and the typical time and cost to charge from 10% to 80%.
- Not on plug-in hybrid reports
Real range estimates
Low, Typical and High range figures, from winter motorway driving to summer town driving.
- Not on plug-in hybrid reports
Range over time
How your range is likely to change as the car gets older, based on ClearWatt data from similar vehicles.
- Not on plug-in hybrid reports
Battery warranty
When your battery capacity warranty ends, and how much time and mileage it has left.
Why your result matters
The battery is the most valuable part of an electric car. Knowing its condition helps you every day you own it, and on the day you sell it.
Know the range you can count on
Plan journeys with range figures for real conditions, not just the official lab number.
Catch problems while you are covered
Most EV batteries have their own capacity warranty. Testing while it is still running means any issue can be raised while cover is in place.
Back up your car’s value
Battery condition is the first thing buyers ask about a used EV. A dated report gives you evidence when you sell or part-exchange.
See how your battery ages
Batteries change slowly over time. Testing once a year, for example at your annual service, shows how yours is holding up.
Common questions
Do I need to do anything?
No. Your dealer runs the test while your car is with them, for example during a service. The car just needs to be parked and switched on.
Does the test change anything on my car?
No. The test only reads information from the car. It does not change any settings or software.
How do I get my report?
When the test is complete, ClearWatt sends the report to your dealer, who shares it with you. A small number of results are checked by the ClearWatt team before release, which can take a little longer.
How often should I have my battery tested?
Once a year is a good rhythm, and it fits neatly with an annual service. Each test adds to the picture of how your battery is ageing.
Who is ClearWatt?
ClearWatt is an independent UK company that specialises in EV battery health. Your report is not issued by your car’s manufacturer.
Is the report a guarantee?
No. Your report shows the battery’s condition on the day it was tested and is for information only. It does not guarantee how the battery will perform in future.
Questions about your result?
Your dealer can talk you through your report. For more on the readings behind it, read our detailed guide to the EV Flash Test.