The following instructable demonstrates how to make a 3 x AA battery holder for mounting onto a bicycle frame. To construct it you will require the following:

Materials:

1 of spring material
1 of sheet metal 3 1/16" x 3"
1 of 1/2" PVC nipple 6" length
2 of 1/2" PVC threaded caps
2 of #10-24 machine screws
2 of #10-24 hex nuts
2 of #10-24 wing nuts
4 of #10 washers
4 of pipe clamps

Tools:

Index Card
Pencil
Right Angle
Sandpaper
Drill Press
#10-24 Screw Tap
Drill Bit
Screwdriver
Wrench
Masking Tape
Red Sharpie
Black Sharpie
Foam Tape
Friction Tape

Note:

#10 sized screws were selected because they can fit crimpable ring terminals.

Step 1: Create Drilling Template

To make a terminal, a center hole must be drilled into the PVC cap. A template is used to accurately drill through the center. The following steps are documented in the attached images:

Using an index card and triangle tool:

1. Put the PVC cap onto the middle of the index card, don't worry about it being perfect.
2. Trace the cap around the index card.
3. Draw tangent lines perpendicular to one another around the traced cap circle.
4. Draw lines from corner to corner of the square formed by the tangent lines.
5. The intersection of these two lines is the center of the traced circle.

Step 2: Drill & Thread Cap

1. Lightly sand the bottom of the caps to even them out.
2. Center the template below the drill press bit.
3. Cover the cap with masking tape to prevent wandering.
4. Drill the cap with an appropriately sized bit at high speed, slowly push down.
5. With no power applied to the drill press, rotate the tap into the newly formed cap-hole.

Step 3: Cap Assembly

1. Drive the machine screw into the cap.
2. Use a screwdriver and wrench to attach the hex nut.
3. Slide on a washer.
4. Slide on the terminal ring / wire.
5. Slide on another washer.
6. Screw on a wingnut.

Step 4: Widening the Inside

Use a 6" PVC pipe or polypropylene riser. Risers are less expensive but are off center. To get a riser to the desired size, score with a utility knife and break away.

To widen the inside of pipe, convert a screwdriver with a good grip into a round sanding tool:

1. Use masking tape to attach tape to the screwdriver.
2. Slowly rotate the tool into the pipe.
3. Test with batteries until they slide through easily.

Note that this process can take a long time (20+ minutes) and the sandpaper may need cleaning off with a brush.

Step 5: Sizing the End Caps

It's important to keep the ends from being too tightly screwed on as they can damage the batteries inside. To decide what a good tightness is:

1. Screw on one of the end caps completely.
2. Put in 3 AA test batteries.
3. Unscrew the end cap until the the top most battery lies below the opening as pictured.
4. The battery should NOT be flush or protruding from the opening.
5. Use threading / plumbing tape to cover off limits threads as pictured.

Step 6: Cartridge Assembly

To assemble the cartridge, you will need:

1 x PVC Nipple
1 x Spring
2 x End Terminals
3 x AA batteries

To color code the cartridge, use:

1 x Red Sharpie
1 x Black Sharpie

For the spring, try finding an OSH (Orchard Supply Hardware) as they distrubute Centry Springs products. You'll probably need to modify the spring a bit, so that it coils towards the center on both ends. The spring I used came from a broken solder sucker tool.

Pictured is how to assemble the cartridge from left to right, top to bottom. After this step, it's ready for testing, and can supply power through its terminals.

Step 7: Shaping Metal Clips

In order to hold the cartridge to the bicycle, you'll need to make holder clips.

Template:

Each holder is 13/16" at the center rectangle with 3/4" wide wings the stretch 1 1/4".

Cutting / Shaping:

1. Use tin snips to cut.
2. Use a rubber mallet & hose clamps to have the base of the holders conform to the bicycle frame.
3. Protect the bicycle frame with masking tape.

Coloring:

I'm fairly certain the temperatures were too low to temper the metal, however. If you're not using a zinc-plated or stainless sheet, you can heat it up on your stove and immerse it in mineral oil. This gives it a black finish.

Step 8: Attaching Clips

To attach the clips:

1. Use friction tape to prevent pipe clamps from scratching the frame surface.
2. Use foam tape underneath the clip to prevent it from scratching the frame.
3. Use pipe clamps to secure the clips to the bicycle frame.