The mobile hotspot is configured (by default) to optimize battery life. There are several methods you can use to extend the battery life:
If the devices you are connecting to your Wi-Fi network are always near the mobile hotspot device, shorten the Wi-Fi range. Home screen > Battery > Wi-Fi Performance
Reduce the amount of time to wait when no devices are connected to either Wi-Fi network before going into standby (Wi-Fi radio powers off). Home screen > Battery > Standby Timer
Reduce the LCD's backlight settings. Home screen > Advanced Settings > Display > Backlight Settings
Set the Display Timeout to a shorter period. Home screen > Advanced Settings > Display > Turn Off backlight