Battery Registration and Coding After Replacement

On an older car, replacing the battery is a matter of two clamps and a bracket. On many newer ones there is a further step that involves no spanner at all, and it is the one most often left out.

The car needs to know that its battery is new. Without being told, it goes on treating a fresh battery as an old one.

What the car is keeping track of

Cars with battery management have a sensor on the battery terminal that measures current, voltage and temperature. From those readings the car estimates the battery's charge and its state of health, and it stores a history that builds up over the battery's life.

The charging strategy follows that history. A new battery is charged one way and an ageing one another, and the car decides when start-stop is allowed and which comfort features to switch off when the battery looks weak.

Registration and coding are different jobs

Registration tells the car that a new battery of the same specification has been fitted. The stored history is cleared and the charging strategy starts again from the beginning.

Coding is needed when the new battery differs from the old one, for example a higher capacity, or AGM where EFB was fitted before. The car's settings are changed to match. Some Audi and Volkswagen batteries carry a code on the label for this purpose, though it is not required in every case.

Which cars need it

The requirement depends on the model and the year, so treat this as a guide and not a rule.

• BMW, Mini and Alpina: nearly always
• Audi, Volkswagen, Seat and Skoda: most models with start-stop or energy management
• Jaguar and Land Rover: most recent models
• Jeep and Mazda: many models with start-stop
• Porsche, Volvo and newer Fords with a battery monitoring system: commonly need a registration or reset
• Most Japanese and Korean saloons without start-stop: no registration needed

What happens if it is skipped

The car will still start and drive, which is why the step gets missed. The effects show later:

• Start-stop stays restricted or switched off
• A battery or charging warning remains on the dash
• The new battery is charged to suit an old one, which can shorten its life
• Comfort features may be limited as though the battery were weak

How it is done

A diagnostic tool is plugged into the car's OBD port, the battery function is selected and the new battery's details are entered. It is done at the car, in the parking bay, straight after the fitting.

A memory keeper is normally connected while the old battery is out, so that the radio, clock and window settings are still there when the new one goes in.

Questions to ask whoever fits your battery

Three questions settle it before any work starts:

• Does my model need registration or coding?
• Do you have the tool to do it at the car, and is it included in the price?
• Is the new battery the same type and capacity as the original, and if not, will the change be coded?