A lot of the micro radios meant for park flyers don't have a separate battery plug because they were meant to be powered by the battery eliminator in the ESC (electronic speed control). You can use a separate battery to power these rceivers by plugging a regular glow plane's reciever battery into the throttle or any other un-used channel. You can even use a Y-harness to plug both the reciever battery and some servo into the same channel.
This is also true of normal radios meant for glow planes. The servo positive and negative wires just hook up to a common rail in the reciever.