Yaboodn Small Digital Clock, 6.5 inch LED Display with Light Blue Digits, 3 Levels Brightness Adjustable, Desk Alarm, Table Clock with 1 Alarm, 12/24H, Temperature, Calendar Corded Powered(Blue)

Here are a few results of installing batteries or plugging in: 1. Battery only --- The clock and alarm will run, just automatically enter the power-saving mode after no operation, i.e. the screen will turn off and enter the background operation. 2. Plug in the USB cable only --- the clock and alarm will run normally, the screen will be on all the time, but there is no time memory function, once the power is off and then plugged in again, you need to reset the time. 3. Install the battery and insert the USB cable -- the clock and alarm will run normally, the screen will be on all the time, and the clock will have a memory function, once the power is off and connected again, you do not need to reset the time. So if you need the screen to stay on all the time, you can plug in the USB cable only or plug in the USB cable and install the battery.