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I believe you have a mild hybrid like the M340i correct? I found this on another BMW forum:

I have successfully charged battery three times (MY21 40i) using the steps below:

1. Start the vehicle and turn off, then turn off the iDrive manually by pressing the volume knob a few seconds. This ensures iDrive go into sleep mode (also known as idle state, see details on this at the end of the post). This seems to be the trick. If you want to be extra careful then use Digital Key Card to do the steps. It removes another variable (comfort access proximity sensors used by key fobs).

2. Open door, exit car, open bonnet, and close door (don't lock yet). Keep the bonnet open until charging is complete (THIS IS A MUST), two U-shaped bonnet latches should not go into the sockets (this is how vehicle knows if the bonnet remains open or not).

3. Connect charger cables in this sequence: positive > negative > charger power.

4. Lock the car. Don't open doors while the car being charged, this might cause charging/battery related error codes being displayed on iDrive later. Note that you might hear a few actuator motors makes brief noises between engine bay and dashboard as if those are trying to open/close something, this is normal. A few LEDs on buttons around driver seat will continue to be illuminated for about 15 minutes and turn off automatically after a while, this is also normal.

5. Move away from the car and don't do anything that might wake up the iDrive.

6. When battery is fully charged disconnect the cables in reverse order: charger power > negative > positive. Close hood/bonnet.

Depending on the charger type and battery charge state it might take long, I usually keep it going overnight.

Hi
As we settle in to Winter, I attached my CTEK 4.3 trickle charger to my 2021 M440i. However, it is not progressing past step 3 (over a week). This worked fine on my 2019 Z4. Anything different about charging this vehicle? Need a different charger?

Thanks...

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