What is the power draw of the iPad Air? I am trying to hook a dragonfly dac to my iPad Air using the lightning to USB3 camera adapter kit.

When powering the camera adapter kit using a backup battery supply that outputs 5V/1000ma, the dragonfly will not work and the iPad says that it draws too much power and will not output sound through the lightning port.

When I use the same configuration but plug the lightning power cable into an electrical outlet, everything works and the DAC captures and processes the sound.

I cannot determine how large a power supply I would need to have the iPad keep working with the dragonfly plugged into the camera adapter kit.
The iPad Air comes with a 11.73 W charger (2.3 A at 5.1 V), so I would go for at least that much.