I received a notification that reported that my sky had gone offline. After looking at wifi and actually making sure it was still mounted, I noticed the battery levels dropped significantly over a a few hours. The battery was steady and reading “Good” levels before.
https://smartweather.weatherflow.com/station/6302/graph/20107/battery/3
You will find several discussions here about how the batteries suddenly die. It’s exactly how they work.
dont worry its a normal end of battery life pattern just replace them , i would say has you hit the 2.70 mark prepare to replace at some stage . or alternatively buy the optional solar panel https://shop.weatherflow.com/products/solar-power-accessory
Good to know. I have already purchased the solar panel. I just need to put the thing on.
The time for that has come 
Got out today (1 degree out) and installed the solar panel onto the Sky. All is good.