The mobile hotspot is configured (by default) to optimize battery life. There are several methods you can use to extend the battery life:
Ensure that the device is charged completely on its first use to prolong battery life.
When not using the device, turn it off to conserve power. From any screen, press and hold the Power key.
Tap Shutdown.
Avoid using Dual-Band Wi-Fi and Guest Wi-Fi when unnecessary.
Reduce the LCD's brightness level. Home screen > Settings > Display > Screen Brightness
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 > Settings > Wi-Fi > Wi-Fi Range
Reduce the amount of time to wait when no devices are connected to either Wi-Fi network before going into sleep mode (Wi-Fi radio powers off). Home screen > Settings > Wi-Fi > Wi-Fi Standby
The more devices connected to the Wi-Fi network the more battery power is consumed.