Sadly, I don't drive my car much these days due to a disability, and the battery was always low/discharged, even though I didn't activate the alarm when parked in the garage. So, after reviewing a few videos online...
I just did a permanent CTEK MXS 5.0 battery charger/tender install on my 2017 M240i. The MXS 5.0 is the go-to model for decent functionality w/o breaking the bank (any lower model and you don't get temperature sensing adjustment and, in some cases, merely tender w/o full charging capability). Sorry no pics, but I will describe what I did...
You can use the wires with the clips (but I wanted a neater, more permanent solution, so use the o-ring wires). You want to install the +ve o-ring wire to the +ve battery terminal under the hood (no, never attach directly to the battery in the trunk, as it could fry sensitive electronics!). I was lucky that my terminal has a removable T-bolt, otherwise you'll have to find another way to make the connection. Then find somewhere nearby to attach the -ve 0-ring (I resorted to sliding the damn thing underneath a small bracket that bends over the edge of the engine body, and may need to solder it eventually, but any connection attached to the body will work). Also, luckily I had a small crease/crevice with which to tuck the -ve o-ring wire, so that it doesn't infringe with the plastic hood bonnet (otherwise you might have contact when closing the hood).
The wires all get covered with 10mm black auto flex tubing (optional and merely for cosmetic reasons). The lead wire gets fished through to the windshield wiper area (so you can close the hood w/o issue). You then simply tie-in from there to the unit, which gets plugged into a power outlet.
I purchased the CTEK extension wire but found I didn't need it. I intend to buy the CTEK plastic holder, so I can mount the unit on the garage wall, and avoid the need for this extension wire or any extension cords.
The total cost for the unit and materials was about $175-$200 CAD. This was a time consuming process simply because it was difficult to locate a suitable body/ground connection point, otherwise you can do it in 15 min. She works like a charm with the hood down, and alarm on! Just remember to lift up the driver's windshield wiper to remind you to unplug the damn thing before you drive off! Any questions; fire away.
