The 9 does not have a dedicated power socket. My technique for many years is to connect one batt, output to ch 1 socket via a ylead, and the other to the 9 ch socket, ie other end of power rail. also via a y lead,. Used that on many Weatronic and now Powerbox receivers, it works, never a problem.
This was recommended to me many years ago by a real expert as it is an application of Kirchoff’s law and doubles the current handling of the power rail.