Beryl + USB iPhone tether + Charge iphone at the same time

I did some checking about the voltage from the router I’ve been trying to use, a Slate. GL-AR750S Slate and power for USB tethering? - #2 by wcs2228

It seems the Slate may not be putting out enough voltage/wattage to keep a tethered phone charged.

I have not found a splitter that works either.