According to headphonics, 70mW on 3.5mm and 120mW on 4.5mm. The newest firmware that I just downloaded (1.0.0.7) had a significant impact decreasing power output on the 3.5mm output - a positive overall for the ultra sensitive Solaris 2020 and Valkyrie. I have no way way of technically measuring and verifying all this but all in all, the S1 is a very low drain on my phone.
Unrelated to power draw: I came across this today which might be helpful to see the effect of the various filters/presets. Coincidentally, this person also describes the “Full Bass” preset as a castration of the mids and trebles. I don’t think there’s a better word for it. One failing of the device is certainly a separate bass boost option.