Besides this, like many I have my doubts about battery power;
My experience with them is mixed:
Because I wanted less noise I made a psu for my tubepreamp which converts 12V from a caravan-battery to 220V.
A lot of capacitance behind it so worked OK. The switching frequency is below the noise.
When I put a AC/DC supply of 12V instead of the battery it sounded really bad.
Back to my old AC/DC 220V supply was really bad too.(and it was supposed to sound very good)
So I settled for the battery, but still some noise, maybe the tubes?
Then an extra AudynCap capacitor close to the battery and a much lower noisefloor!
Now I don't like this because it means I can hear the quality of this capacitor and of the battery...
Besides the overnight charging which I sometimes forget.
So for A DAC it's a nice experiment but not garanteed to work.
If you can make it to work let us know how it sounds!