The battery isn't held down properly, or it's leaking electrolyte. A loose battery can move about and short against the bonnet or bodywork, which is a genuine fire risk, and leaking acid damages everything it touches.
Wording as it commonly appears on an MOT certificate: “Battery insecure or leaking”.
What does it mean?
The battery isn't held down properly, or it's leaking electrolyte. A loose battery can move about and short against the bonnet or bodywork, which is a genuine fire risk, and leaking acid damages everything it touches.
How serious is it?
Usually recorded as: Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- A missing or corroded battery clamp, often left off after a battery change
- A swollen battery case from overcharging or heat
- Corroded terminals letting acid creep out around the posts
What a mechanic would check
Try to move the battery by hand — it shouldn't budge. Then check the case for swelling or damp, the terminals for that white-green fur, and the tray underneath for corrosion, which is where the acid ends up.
What might need replacing
- A battery clamp or hold-down bracket
- A battery, if the case is swollen or leaking
- Terminal clamps and a clean-up of the tray
Can you still drive it?
It's a failure. A loose battery under the bonnet is a fire risk, and it's about the quickest thing on the whole certificate to put right.
Repair cost
A hold-down clamp is a very cheap part. A replacement battery costs more and varies with size and whether the car needs a start-stop AGM type — don't fit a standard battery to a start-stop car.
Before the retest
Battery, wiring and horn faults are usually quick to fix but easy to forget about. Make sure the battery is clamped down so it cannot move, the terminals are tight and there is no fluid leaking. Check that no wiring hangs loose or rubs on moving parts, and that the horn gives a steady, continuous note.
Retest rules
If the vehicle stays at the test centre for repair and is retested within 10 working days, a partial retest is often free; some items qualify for a free retest if you bring the car back by the end of the next working day. The exact conditions are set out on GOV.UK, so confirm with the test centre before you leave. A major or dangerous failure means the car cannot legally be driven away unless the previous MOT is still valid and nothing dangerous was recorded — check your certificate first.
Related help
More electrical failures · MOT failure decoder · Ask a mechanic about your certificate
This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.