I have a set of 20 of the Tello Drones that I purchased from Pitsco. They worked great at the start of the unit but now I have random drones that are now displaying a non-official battery error message on the tello app and will not take off. I can connect to them. I can update firmware and the camera works they just won’t fly.
I would recommend trying a factory reset on those Tellos. You can factory reset Tello by powering up the Tello, waiting for the initial boot sequence to complete, and then holding the power button for 15 seconds and Tello should reboot automatically.