To maximize security for emergency backup, this level should be set a high percentage. A high power reserve percentage keeps the batteries toped off for emergency backup situations.
The Enable Emergency Power Reserve feature temporarily sets this to the highest security level for a defined period of time. At the end of the defined period of time, the power reserve level will automatically go back to the default value set be the user prior to the event. This feature was designed to be used when alerted of a storm warning, natural disaster, or other event in your local area.