Will a dead battery fail the MOT test?

The MOT test is a thorough set of inspections which will determine whether or not your car is fit and safe for the road.

When considering a flat or dead battery and the effect this has on the outcome of the MOT test, it is not a cut-and-dry answer.

In short, yes, a dead battery can result in an MOT test failure. But not in isolation. The failure would come under some specific circumstances.

Mandatory Lighting and Electrical Systems Check

As part of the regulations and according to the UK Government’s official MOT inspection manual, vehicles must have functioning electrical systems for the test to be carried out.

This includes:

1. Headlights, indicators, and brake lights
2. Dashboard warning lights
3. Horn and windscreen wipers

Now, should the battery of your car be dead and therefore unable to start the car, these components cannot be powered during the test.

In this instance, the vehicle would be classed as "refusal to test". That is to say, the test cannot proceed.

Which effectively means it fails to complete the test.

If the test is able to go ahead and the electrical components do not function due to the battery, it will be marked as a fail.

Battery Mounting and Security Requirements

Another part of the MOT regulations also states that the battery must be:

• Securely mounted
• Free from leaks or visible damage

In the case of a dead battery, this itself isn’t an automatic fail if it can be jump-started for testing and all electrical systems operate correctly.

However, should the battery be leaking acid or visibly unsafe, it will be marked as a major defect, which does result in a fail.

Emissions and Engine Start Requirements

As we’ve already touched upon, a flat battery can prevent the vehicle from starting. If the vehicle cannot be started:

• The emissions test cannot be conducted, which is a mandatory part of the MOT.
• This will again result in the test being refused or failed.

Prevent Dead Car Battery

To prevent a dead car battery, drive your vehicle regularly for at least 20–30 minutes to keep the battery charged, especially if it's usually left unused.

If your vehicle is not going to be driven for a long period of time, you can use smart trickle charger.

Try to keep the terminals on the battery clean and free from corrosion. This helps to maintain a strong electrical connection.

Finally, and this may seem obvious, but where possible, avoid using electronics like lights or the radio when the engine is off.

These will drain the battery over time.

Dead Car Battery and the MOT

So, while a dead battery in isolation is not a listed failure item in MOT criteria, it does have a domino effect.

If the battery being flat stops the car from starting or powering essential systems, the vehicle either cannot be tested or will fail due to the components not working correctly.