If you want to build a circuit, you will need to power it somehow. You could buy a battery holder locally for up to $2, or maybe even more. If you want something more exotic, like a 4.5 volt or 7.5 volt pack, it will cost more. 9volt battery snaps are relatively easy to buy, and pretty easy to make as well. Here we will make a 3 volt battery pack out of tin foil, duct tape and a bit of stranded wire.

Materials

About a foot of duct tape

Tin foil, less than you would use to wrap a sandwich

Two AA batteries

rubber band or zip tie

Two segments of stranded wire, about 4 inches or longer

Tools

utility knife or scissors

Wire strippers

Ball point pen or permanent marker

Process

Make tape cylinders

Cut 3 segments of duct tape, about 3 1/2 inches each.

Cut a square off of one end of each. The cut out segment should be half as wide as the tape.

Lay the duct tape on the table with the sticky face up.

Fold the tape in half onto itself so that all the adhesive is covered except the end matching the cutout. Make sure that none of the adhesive is exposed other than the end .

Roll this tape onto the battery, as tight as possible, with the adhesive tab holding it in place.

Do this three times. One will be a coupler, the other two will go on the positive and negative ends of the battery pack

Make a coupler

Place one of the cylinders on the end of a battery with about half of the cylinder on the battery.

Loosely crumple up a 1"x1" or so square of tin foil and put it in the cylinder.

Push the other battery into the coupler, squishing the foil down to the shape of the battery ends.

Cut four 1/4" by 1 inch strips of tape

Secure the coupler onto the ends of the battery so that the battery stays in good contact with the foil

Make an end cap

Place a cylinder on a battery, about 2/3s on.

Fold up some tin foil, you will need about 2 inches, it should be about 1/4' to 3/8" wide, then fold it over onto itself about three or four times.

Loosely crumple up a 1"x1" or so square of tin foil and put it in the cylinder.

Place the folded tin foil so that it hangs out of the end.

Cover the end of the battery with a segment of tape about 3/8" by 1"

Secure the end cap onto the battery with several segments of 1/4" x 1" tape so that the end cap stays in good contact with the foil.

Label the end caps for Positive (+) or Negative (-)

Connect the foil to the wire

Strip 3/8" to 1/2" off the ends of the wire.

Open up the strands of the wire and wrap it into the tin foil

Cover this with tape so that it does not come loose.

Finalize the build

Test the battery pack with a multimeter.

You should get a voltage reading of 3 volts for fresh alkaline batteries and 2.4 volts for rechargable batteries.

Wrap the pack end to end with rubber band or zip tie so that the ends of the batteries stay in good contact with the foil.

Use your battery pack in a circuit.

If you want to get 4.5, 6, 7.5, 9volts, etc, you can add a coupler for each battery you want to add to your pack.