If you are constantly having problems with Optima batteries you have to look in the mirror for the problem. I sell 1000+ of them at work a year and they are very trouble free. We get several people bringing them in that say they are bad but they just need properly charged. It is always the race car or show car guy having problems with them.
Considering you live in an area that barely gets frost in the winter let alone deep snow, that kind of comment would be expected from this stupid forum. Maybe use google and see what our winter temps drop to here....I had two frosts just two weeks ago in what most consider summer time already...Winter here is way colder than what you get...So maybe you need to look at a thermometer instead of a mirror. I have plenty of battery chargers...2 big "smart" ones, trickle chargers etc.....The solar ones, for what ever reason, seem to work best for long term storage. Our winter temps can last a long time depending on the jet stream, and is nothing to fool with.
I would like to know why batteries do not hold up to the cold some day...They only do if you use them every couple of days, but when just stored, I don't care if they are lithium, AGM, or lead acid....I lose one or two each winter.
https://abcnews.go.com/US/buffalos-deadly-blizzard-numbers-made-storm-historic/story?id=95945684