Rather than worry about the USB port on the charge controller, you will probably have better luck running 12v from the output, or the battery it is charging, to one of these, mounted somewhere close to the RShake.
These work fine. There is a discussion about using these here:
I designed a custom Pi HAT that monitors the (solar-source) battery supply and gracefully shuts down and restarts the Shake’s Raspberry Pi in the event that the batteries get too depleted. This prevents data corruption when the Pi is otherwise running under voltage. FYI, this was created to solve this very problem that was occurring on the Shake I was using which is solar powered. You can message me if you would like to purchase one.