I made the change to lithium 4 years ago and have been pleased with the change. While it is getting a bit dated,
here is the documentation of the change, although prices have come down, particularly if you look at sources other than Battleborn. I currently winter camp, but it is at Quartzsite, AZ with temperatures rarely going below freezing, and daytime temperatures in the 50's or above.
That said, I have followed your adventures, and you do enough cold weather camping that I'd be concerned about charging. While the lithium battery will be OK discharging down to -4*F or so, as others have pointed out they should not be charged below 32°F. Heated batteries are a solution, but you still need to find the energy to heat them.
You mentioned days only going up to 30°F with 10° nights - it may be tough to carry enough solar to bring the battery up to charging temperatures after a 10°F night. Unless you carry a generator, a couple of cloudy days may leave you unable to catch up.
