Battery Saver stuck on

My watch display was very dim this morning with just a minimal digital time on it. It had plenty of charge (60%). I finally went into the settings and the Battery Saver was on, also displaying "(10 Days)". When I turned it off manually that changed to "(9 Days)". What does that mean?

I thought that the saver was supposed to come on automatically when below a certain battery percentage, so am not sure what happened here. Maybe a recent software update changed something? Anyway it's working correctly now.