[MilehighM3]

Originally Posted by Teutonic

My 2012 X1 uses the 2012 OEM BMW trickle charger [deltran) and works fine.
I can also use the CTEK and the Noco 5 with the X1.

The 2021 X4 and the 2021 M340i don't work with the CTEK. They are both MHT vehicles.
I believe that the X4 works with the Noco5 now..? Not sure, I need to try it again.

The M340i does not accept any of the chargers via under the hood, all of them induce the same behaviour with a small motor noise followed by a clicking noise on the 48V battery area. (Unfortunatley we can not post videos in this forum).

I believe that the small 48V battery is more than $1500 but I might be wrong.

As mentioned above, my shop foreman tried two other brand new 2021 M340i from the dealer's lot and all behave absolutely identical with sam noise and same click.
They all charge however with the professional BMW shop charger via under the hood. The tech could not explain why this happens. All chargers are BMW oem except the Noco5 which I bought it as I thought it will do the job.

As my situation was desperate I disconnected my M340i trunk battery and charged it with Noco 5 directly with no issues.
Under the hood method however, doesn't work. As you can read on my previous post, there is a link where other members whee in a same situation with MHT vehicles.
Is just that is annoying and not practical whatsoever.

I am still looking for the proper answer in regards with this.

A couple things come to mind. First off, did you disconnect the 48v battery before disconnecting the 12v on your 340? If not, reconnect the 12v and disconnect it first. This is a requirement to prevent damage to the 48v battery.

The reason I asked for battery charger location is relevant if you know how the 48v system operates. With the hood open the 48v system is de-energized automatically. To charge the 12v via the engine compartment requires at least 30a charger, your local foreman should know this.

Try disconnecting the low voltage/communication connection on the 48v battery. This is done by removing the cover over the 48v battery and locating the connector on the outside of the battery. Pull back the grey secondary lock on the connector by pulling back until it clicks, then releasing the primary lock by pinching the connector in the center downward with your thumb and pulling back. I can post a video if needed. Then connect your maintainer to the connection under the hood, careful to make sure nothing sticks up to contact the hood, and close the hood. See if the charger works this way.

You're close on the 48v cost, it's around 2k and takes a few hours labor to replace along with some coolant since it is liquid cooled.

There's also a way to charge the 48v battery via running the engine that you should be aware of if your vehicle is stored. A 12v charger cannot charge the 48v battery. It's in print that it can, but I've tested several cars and it does not change. Bring up the vehicle info in the idrive and access the power flow. Here you'll be able to see the battery charge level which is indicated by the ratio of blue sectors to black/empty. You want 2-3 sectors to be blue, indicating 40-60% charge. Put the vehicle in sport mode so you can see the tachometer and rev the engine to 3-4k until you see power flow being sent to the battery. Hold the RPMs at the point where the charging is operational until the desired charge level is achieved. I can post screenshots/videos as needed of these steps as well later today.

Sent via mobile please excuse my typos