The M1 Caliber runs off of 2 AA batteries. The LCD-Backlight on time with standard batteries is approximately 15 hours. However, there is both an automatic standby and automatic shutoff built in to every M1 to help conserve power. In practice, a single pair of batteries may last several weeks depending on use.
Automatic Standby - M1 goes into standby mode after approximately 3 minutes and turns off the backlight. Moving the wheel or selecting any button will wake the M1.
Automatic Shutoff - M1 shuts off after 5 minutes of inactivity. Use the power button to turn back on.