Now we can work on making the battery pack to give us portable power. Grab the remaining parts you'll need, the battery holder, diode, long battery connection cable, and small heatshrink.
Cut the red wire of the battery pack short by about an inch.
Then strip and tin the wire.
Find the diode, this part will protect the board in case you put the batteries in backwards, it also lowers the voltage a little so if you have fresh alkaline batteries, the voltage won't be too high. Diodes are directional so make sure you're working with the right end. Find the end that doesn't have a white strip and cut it short. Solder that end to the red wire.
Clip the other side (the side with a white stripe).
Cut off and slide a ~2" piece of black heatshrink onto the red wire past the diode.
Now solder one wire from the battery connection cable onto the other end of the diode, you may need to tin both if you are having trouble getting a good joint. It doesn't matter which wire you choose so just pick one!
Slide the heatshrink back over the diode and solder joints.
Now shrink the tubing to protect the diode, you can use a hair dryer, heat gun, lighter or the edge of your soldering iron.
Now we'll connect the other side of the long power cable to the black wire. Slide a small 1" piece of heat shrink onto the black wire (this image shows a much shorter piece, but its too short so go a little longer).
…and solder together the wires
Then heatshrink like you did before!