Just to update everyone with my battery problem. I kept the battery plugged in my smart charger over the winter. Since then, I've been using my bike almost every day with no issues for the past 5 weeks. I've been regularly checking the voltage on the battery on the TFT screeen and while the bike is running, it steadily stays above 14V and when engine is off it never goes below 12V.
So really nothing to explain my problems last year. I'll update is thing change.