I can count on one hand the number of audio interfaces that have battery power built-in (and they use AA iirc) @vehka and they are from Apogee, and only work with iOS and OS X. And they are pricey. And a quick Google search does not show anything for Linux on the current models.
Chances are very low that you will get phantom power if you manage to find an interface that is powered by the meager 100mA that Apple allows the iPad to power something with. Phantom power is in the single digits mA-wise, but that’s going to take roughly 290mW to power one mic and you have 500mW total on the connection before any conversion/loss (V x A = W). It could take less power, I calculated off the high end I’ve seen of 6mA.
Someone on the Auria board mentioned the Blackjack worked ‘out of the box’ with their iPad, and didn’t mention powering it externally (doesn’t mean they didn’t).
Here’s the setup someone is using to power a Focusrite interface:
Sometimes you have to make a little sacrifice to get what you want 