I've used separate warm batteries, newly bought original ones, swapped batteries when errors occurred etc, errors occur when battery meter shows full battery. Quite sure it's not the battery.
I'm very familiar with condensation issues, I've used cameras and electronics in cold conditions quite extensively. I keep the gear in the closed bag to cool down and warm up slowly to avoid condensation. In the climate I live in condensation is rather easy to avoid, the air is generally rather dry both summer and winter.
I've used one other back (an ancient Hasselblad CF22, also open vent and fan) with the exact same tech camera with the exact same procedures in the same type of conditions many times without any problems. And of course I use my DSLR (a 5Dmk2, ie consumer level sealing) in the same way, without problems.
So I'm quite sure there's some specific issue with this back. Fortunately Leaf centrally has listened to my elaborate description of the problem and decided to take yet another look at this. It's not supposed to be this dodgy under these conditions. I don't yet know what the result of that will be. I hope they will be able to reproduce the problem. I experience problems about 6-7 out of 10 times out in chilly/cold weather, so there are 3-4 out of 10 that is trouble-free. This means that the problem is not super-easy to reproduce at will, but if you work with the back over a few days you get failures. I'm not a studio photographer that can pick a backup off the shelf, as I go to fairly remote areas by foot I need a back that I can rely on.
My guess is that there's one or more components in the back that has a rather small tolerance range, and due to sample variation some units work well and others are be a bit unstable, ie my back is not necessarily faulty but happens to have tolerance on the wrong side (this is also what P1 web support suggested). Not great if that is the case, but I would guess less than 10% of medium format shooters use their gear in "tough" conditions so few would notice, and as long as Leaf helps out us few winter outdoor photographers to get a unit that is stable outside studio conditions I'm good.