If an AirVisual Pro is kept disconnected from power for an extended period of time, the battery may not charge normally when AC power is applied again. This problem occurs due to a synchronization mismatch between the battery cell and firmware.
In this case, you may notice that your AirVisual Pro immediately powers off when the charging cable is removed, and the battery icon continuously reads '0%,' even when plugged in.
To return your AirVisual Pro's battery to peak-performance, turn your AirVisual Pro off for 2 solid minutes, and then leave powered off while the device charges for 30+ minutes. This will allow the battery to reach an important 3.6V threshold, after which the device will begin to behave normally again.
To read more about how to get the most out of your AirVisual battery, see the link below:
https://www.iqair.com/us/newsroom/how-can-i-get-the-most-from-my-airvisual-pro-s-battery