In the next step, we will attach the Q Brain four-in-one ESC to the quadcopter frame. But, before we can do that, we will just need to solder a battery connector to the battery leads of the Q Brain.
So, while your soldering iron is heating up, you will need to determine the orientation of the plug. In other words, since the plug is polarized (it will only work in one direction) you need to know which wire attaches to which plug pole. The battery plugs - which, by the way, are called XT60 plugs - are shaped like arrows, with a flat end and a pointy end. The red wire from the Q Brain should be soldered to the flat end of the plug and the black wire should be soldered to the pointy side.
Now to the actual soldering process. First, slip a ½” piece of shrink tubing over each of the Q Brain’s battery leads. Then, using care because soldering irons are obviously very hot, solder the Q Brain battery leads to the XT60 plug in the order mentioned above. Then, after giving the solder a couple minutes to cool, slip the sections of shrink tubing over the solder connections. Finally, apply some heat, with a heat gun, or a lighter, or even a match, to the shrink tubing to finish the battery connection.