I noted in a previous post, https://www.steinberg.net/forums/viewtopic.php?f=183&t=95419 , that Apple have released a new adapter that allows the iPad to be charged at the same time as it is used for transferring data. I have now been using this adapter with an iPad and the Steinberg UR22mkII audio / midi interface.
One side of the adapter was connected to the lightning port on an iPad (4th generation). On the other side of the adapter, with both lightning and USB ports, the connections were as follows. To the lightning port was connected either (i) a battery pack (Anker PowerCore+ 20100 USB-C) or (ii) an Apple 12W USB Power Adapter. To the USB port was connected the UR22mkII (using the USB2.0 port on the Steinberg interface). The power source selector on the UR22mkII was set to the USB 2.0 side. A keyboard was connected to the UR22mkII via a midi cable, and output was monitored on headphones from the UR22mkII.
In operation, the single power source powers both the iPad and the UR22mkII. However, I found while using Cubasis that the iPad failed to charge up: the charge remained constant over about 20 minutes. It appears that in this mode the combined power demands of the iPad and the UR22mkII approximately equal the 12 W of the power supply. However, if a second power supply is used and connected to the UR22mkII USB-C input (and the power switch set to that side) the iPad will then charge up.
Overall, use of the new Lightning to USB 3 camera adapter allows Cubasis to be used on an iPad, connected to an audio interface, without the risk of the iPad running out of charge.