Hi,
I have the latest 12speed 105 di2.
It's less than a year old and battery states it was manufactured early 2025.
I had been happily using the bike since summer (june / july time) with no problems, only recharging once every 2 months or before a large event.

It has since been put in the garage for two months with only a few uses each month, however the derailleur shows green for 5 or 6 days after charging then suddenly you get no battery light or shifting, I have tried re-charging several times, each time after a few days it is suddenly dead! The garage is fairly well insulated and is not much below room temperature all year around.
I've taken out the battery from the seatpost and checked all connections but there doesn't seem an obvious issue.
Is it the battery? the derailleur? or something else all together?
Any ideas or assistance would be greatly appreciated.