I do not understand what is "time until empty" what is the difference with the alarm?
If I understand the question which is questionable my best guess at a answer is - The battery life is impacted by the use of alarms, the frequency of them, whether you have vibration or tone or both on, how long it takes you to stop the alarm etc. I can't imagine it's a noticeable impact but because it can't be calculated due to the human factoe it's just listed as having some impact?
In the power modes for an activity it will display a battery estimate which will show you the approximate battery life for the activity you have selected. I'm not sure this is what you are referring to though. Would you be able to take a picture of your watch to help clarify what you are asking about?
Did it show "time until empty" after you selected "Low battery Alert"? It looks like that should be the same setting but the wording changed. If that is what happened then what language is your watch set to and what software version is your watch on?
By default I am in French, and yes the title on the screen before selected is not the same it is auto enable which becomes Time until Empty.
But I just understand with English.
It is a time to define the change of battery mode.
Example if there is 15 minutes of battery remaining or can tell the watch to change the mode.
It's just that I was on disabled and that the labels were not very meaningful.
Ahh okay, I misunderstood you then. You are correct, the Low battery Alert will display an alert when you have a set amount of battery remaining and prompt you to enable battery saving mode. The auto enable will automatically enable battery saving mode when you have a set amount of battery remaining or "time until empty".