I have spent my life in a northern climate, and have become used to cold weather. You have to, or else you get cabin fever and brain damage from watching television. You just have to dress warm, dress your metal detector and find a nice place to hunt.
You have to somehow keep your batteries warm. Extreme cold is very hard on batteries, especially 9 volt batteries. The only exceptions are energizer batteries which will hold a voltage in extreme cold. So if your machine or pin pointer has to be manually tuned, expect problems as the temperatures cool the batteries. Also, detectors using knobs don't fair well either. I have had the knobs seize up on my other detectors, rendering them useless in the cold, and electronic pin-pointers unable to be manually tuned in the cold. I have been hunting in the cold for about 20 years, and find the push button adjusting metal detectors far superior when hunting in the extreme cold.
To keep my rechargeables working a long time, I tape a hot pac on the outside of the housing above the batteries, then put a cover over the housing, stuff the inside with Kleenex, then close it. This works great!
I drove to a snow hill close to home and hunted for about 3 hours. This hill gets used by kids sliding down on pizza boxes, toboggans, snow boards and other gizmos. My first shallow target turned out to be a nickel. I got a toonie (2 dollar coin) on the right photo, a welcomed find! Overall, I had a great day and came home with some loot, as shown below.