Maintaining batteries can be tricky if the weather doesn’t permit us from practicing our hobby over extended periods of time. 2021 was an exceptionally bad year for astronomy. Wildfires, wet winter with lots of precipitation and snow in the mountains. Unfortunately deep cycle batteries need to be taken care of and not allow them discharge below 20% of their capacity. It should be enough letting them charge over a couple of hours once a month. Unfortunately, just like many other users, I forgot to follow that routine, ending up with a dead battery. The replacement process is easy when you follow this YouTube guide below from another fellow astronomer.
I ended up buying the Duracell (DURDC12-20NB) battery instead which made it of course an upgrade.