If you always get the message that the device has too little power despite being fully charged, then I think it could be faulty.
The device must be fully chargeable.

As other commenters have already written, you must first fully charge the device. The device only runs via a power cable. The battery only serves as protection against power failure or if the device should suddenly run out of power.

The device must be charged for several hours before use. The charged battery provides protection in the event of a power failure.

The device must be fully charged beforehand. The error message will then disappear.