Suggest providing a video of the problem for us to see.
What is the voltage of the battery measured when the low voltage prompt appears.
Did you fully charge the battery,? Does the Raspberry Pi also show the low voltage prompt when fully charged.
Have you fully charged the battery and then connected the PiPower to the PI4 to start it? Are you seeing any low voltage warnings?
When the battery voltage is too low, a low voltage warning will indeed appear.
If you are playing while charging, with the PiPower connected to a power source, it’s recommended to use the official 5V 3A power supply from Raspberry Pi.
Using a third-party power supply may also result in low voltage warnings.
Yes official power supply works fine. No warnings. I get 5,18V on it. When I put the pipower in between it only outputs 4,7-4,8V when fully charged. When I unplug it from AC the voltage goes to 5V.
The warnings on home assistant are when using the pipower. Afterwards is on the official supply.