pre-conditioning on home charger (normal socket, not fast)

hi, I have a 2015 Rex (since 1st January) and am trying to ascertain whether I can pre-condition the battery (not the cabin) via the slow charging, standard cable going into a normal household powerpoint? My dealer doesn't know ...

Yes, definitely.

The battery pre-conditioning takes a lot of energy, I believe up to 3kWh, and some owners have calculated higher. The system pulls it from the battery no matter what. Being plugged in is just a requirement.

On the 120v setup it'll go into charge deficit. I see this every cold night when I leave work, where I happy plug away at about 5% per hour gain, but then the last few hours charging progress stops or stumbles depending how cold it is.

Edit: link
https://bmwi3owner.com/2016/01/preconditioning/

Battery conditioning, as started when you set a departure time, runs the 1Kw heater. But, if you also check the cabin preconditioning, I've seen the system drawing nearly 3Kw. Depending on the year and where you are, the OUC plugged into 120vac is at most a 12A device, so 12*120vac=1,440W. It should run the battery heater without affecting the battery charge. But, if you also want the cabin conditioned, you will not leave with a full battery.

Do you have plans to get a level 2 charger? It can make life much easier knowing that even if you get in late at night, you can still leave with a full charge in the morning, or that during a lunch hour at home, you can get in an additional 20 miles or so.