The Parrot Skycontroller USA has two batteries - one for the controller itself and one for the integrated tablet. We only display the battery percentage for the integrated tablet in DroneSense.
The Skycontroller USA enters into what's called "wintering mode" if it's not used for 7-10 days (depending on battery drain). Once the controller enters wintering mode, it must be plugged into wall power via the USB-C charger for at least 10-15 seconds. Otherwise, the controller won't power on, even though the tablet will power on.
This means you can log into the DroneSense app on the integrated tablet, but nothing will happen because the controller isn't actually turned on. A flashing blue light means the controller is powered on (the light turns solid blue once connected to the drone). If there's no blue light on the controller it is not powered on, even though the tablet is powered on.
The Anafi aircraft batteries have the same feature and if stored for 7-10 days will not turn on or allow the user to check power levels without first being plugged into a USB-C charger for at least 10-15 seconds.