Step 1: Gather Ye Materials
2 C-cells (this instructable will probably work with D cells and other sizes too).
A few lengths of wire. I used 22AWG solid core. Stranded core probably will not be as successful.
The plastic packaging from your batteries.
Step 2: Connect Terminals
You may find it easier to make these holes if you cut the end of the wire at an angle using the wire-cutters.
Poke one end of the wire through the hole in each side of the plastic holder, then bend into a nub or coil into a short spring-like structure. Make the length of the nub about half the length of the bared wire. This will hold the wire in position and provide enough force to hold the battery against the connection at the other end once in place.
For the top connections, take some longer pieces of wire - 6-8 inches/ 15 - 20cm. I suggest red and black for positive/ negative, but use whatever local conventions are in place. Strip one end of each piece to about 1/4 inch/ 5mm, or whatever makes sense to you - these ends will become the connections to your breadboard or circuit or whatever. Strip the other end of each piece to about 3/4 inch/ 2cm. Coil these ends into a spring shape, and poke each through the corresponding hole in the top of the plastic battery holder. You may need to work the wire in spirals to get it through.
Step 3: Secure Wires
I used this setup to successfully power a couple of test circuits on a breadboard, as well as a temporary replacement for a circuit-mounted store-bought battery clip that got broken. It worked so well in the latter role that I just hot-glued it and left it in place. Battery replacement is quick and simple! It should work well in any situation where vibration is not a problem.