Interestingly, I put a lithium-ion battery for my motorcycle which is amazing. I disconnected the battery terminal last fall. I didn't charge the battery all winter and it was left outside. Yesterday I hooked up the terminal and it started the bike after almost 5 months untended and in sub zero temps. Maybe BMW needs to replace it's AGM batteries with light weight lithium-ion.
Here is a video I made of the first start... temps were -5c the night before. The old bike is somewhat temperamental being air cooled and carbureted.