Some receivers have a little diagram as to what goes where. In the case of the picture below, this is a Spektrum receiver with a little diagram on th side showing what goes where for servos. The Battery Red and Battery Black.. may be Battery Red and Battery Brown.. but it is pretty clearly spelled out.

Some other receivers have a separate battery connection. The Spektrum AR7000 does as does some of the Airtronics receivers. But, the battery can go in any of the vacant slots as long as the polarity is observed. Battery + and Battery - have to match up with whatever the receiver slot requires. For the battery, there will be no 'servo' connection. Just two wires, red and black, or red and brown, and some may be white and black. Just make sure that they match. The manual should clearly spell that out.

CGr.