I use my InReach for satellite communications. The emergency communication feature is the primary reason I got the InReach, and I also use it to let people know my whereabouts, do simple texting, and get weather forecasts.
I typically get ten days on a single charge.
Turn Off Tracking / Use Extended Tracking
Tracking uses lots of power as the InReach marks locations and uploads. There are different tracking intervals, but I turn all tracking off.
Press OK ⇒ Setup ⇒ Tracking ⇒ Send Interval ⇒ Off
Press OK ⇒ Setup ⇒ Tracking ⇒ Log Interval ⇒ Off
Press OK ⇒ Setup ⇒ Tracking ⇒ Auto Track ⇒ Off
Press OK ⇒ Setup ⇒ Tracking ⇒ Ext. Tracking ⇒ Off
Set Backlight Brightness and Timeout
Press OK ⇒ Setup ⇒ Display ⇒ Brightness ⇒ Off
Press OK ⇒ Setup ⇒ Display ⇒ Timeout ⇒ 15 sec
Turn Off Bluetooth
The InReach uses Bluetooth to connect to a smartphone and some sensor devices.
Press OK ⇒ Setup ⇒ Bluetooth ⇒ Off
Turn Off ANT+
ANT+ is a connection technology Garmin invented to connect to Garmin sensors.
Press OK ⇒ Setup ⇒ ANT+ ⇒ Off
Update
Keep the firmware on the InReach up to date to take advantage of new power efficiencies. Use the Garmin Express app to update the firmware on the InReach device.