Haven't tried this yet on my Xperia phone but on my HTC One before I could charge another phone using OTG. Well I was attempting to mount a cheap tablet(with no microsd card and bluetooth) to my phone so I could copy some files and it didn't work but it charged the tablet instead
That's actually interesting. Which tablet is it with what rom/kernel? I could try to modify OTG interface on the Z1 or disable data transfer on the device that's meant to be charged, so you could switch between charging/data transfer. I thought that's not possible to charge a phone with another.