Do you need to back up the power when replacing the battery in a BMW E91?

BMW driver question

Reading your articles about batteries, I know that you need to code a new battery. Now I have a question about its physical replacement. Can it be unplugged, removed and a new one inserted? Does the vehicle need to have power backup through a charger, for example?

I have read various articles about errors with CAS when the battery is disconnected and would like your opinion on this. Also, a few months ago I had a charging problem. The voltage was around 15.2 volts, and after driving a short distance it dropped to 14.4 volts.

Now the charging norm is 14.7 – 14.9 V. This is what I have every time regardless of the distance. Could this be the fault of the old battery (it’s about 6 years old)? Or a voltage regulator or something else?

The problem was on a 2006 BMW 3 E91 with a 2.0 diesel engine, but it may also occur on other models.

BM Cars service response

Replacement of a battery in a BMW should be carried out by a service center with the appropriate knowledge and experience. For E-series cars, it is not necessary to maintain voltage during the battery replacement itself.

However, it is necessary to remove the key from the ignition to prevent decoding of the key and CAS module. Replacing the battery without backup will erase the vehicle’s individual settings, such as:

• locking after starting,
• selective door opening,
• radio station settings,
• memory of seats and mirrors.

If you want to keep these settings, it is necessary to sustain the voltage during the replacement. Alternator charging above 15 volts indicates a problem with the voltage regulator. It is necessary to check the alternator on a measuring table and repair it accordingly.

You are welcome to use our service.

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