This OEM ResMed DC cable is required to connect any of the S9 Series ResMed CPAP or VPAP machines to the ResMed Power Station (RPS) II. The Resmed S9 power cord is 45 inches long and has the proper attachment to connect directly to the back of any S9 machine. The other end of the DC cable connects to the ResMed Power Station (RPS) II. The ResMed Power Station (RPS) II is an extremely small lithium-ion battery that is capable of providing over 20 hours of run time.