Assuming it's the same Eberspacher that goes in the Cali ....
Battery drain is minimal once running .... the big surge is on fire up. An overnight van heat and I would probably note about a 10% drop in battery capacity, although the Cali does have 2 leisure batteries so on the MP that may be a little more, but 10% is with fridge on, tap on and off as I make numerous cups of teas, lights on etc.
A winters night can be anything, for me, from minus 15 to 15 ...... take minus 15, which I had in Scotland 2015, I had it on setting 2 (Cali control panel is 1 - 10 so think 2/10) overnight, sleeping downstairs, and was more than warm underneath my 4.5 tog duvet. On setting two it was firing off and on all night, off more than on, and the van will be chilly when crawling out of the duvet, for example to attend to "biological needs"
. Diesel consumption was minimal, probably a couple of litres, even on highest setting it only burns 0.4L per hour at minus temperatures.
The big thing with winters nights is the length of darkness. Lights on from around 4pm (even earlier if further North than Hadrians wall ) and that's the big drain. You will also want more van heat evening rather than night. Sat up, with me listening to the radio and writing, cold air coming in through the roof vents, only so many fleeces that you can wear at once, and you need more heat than when snug and comfortable under a duvet.
Over freezing, like now, 6 degrees, 4/10 will keep me warm in the van for living in, 2/10 probably too warm for sleeping in.
Upstairs a different story: The heat struggles to rise up there. You need to find one of the DIY methods that channel it up. It also depends on whether you have a roof topper or not. If sleeping upstairs it makes a big difference.
