Disclaimer: I will properly fuse and mount it in an enclosure. For the time being, don't worry, this is in a tupperware so that neither me nor my cats can put their paws on the exposed live wires.

Every time I have to solder one of these I end up with the wrong plug on the wrong cable. The fact that the male metal plug goes in the female plastic plug confuses me. At least positive/negative are on the proper side, just don't connect a battery directly to a power supply or another battery by mistake.