You easely can make a 18650 battery holder from some PET bottles.
What you need:
- 18650 battery /from old laptop/
- 4 PET bottle
- hot glue gun
- scissors+ box cutter
- saw + abrasive paper
- some wire and battery contacts /from kid old game/
- soldering iron
Step 1: The Body
Cut the neck of the PET bottle. Make it with the abrasive paper or the box cutter. You need 4 neck for a battery. Cut a 4cm*8cm rectangle from the PET body. Make a cylinder from it. Pull on the necks to the cylinder and glue.
Step 2: The Tops
Make a hole on the battle tops. Put over the wire and soldering the battery contacts. Glue the contacts to the tops – just in case. Put on the battey and it is done. I use it for a headlamp,a flashlight and a bicycle lamp. If you use enough hot glue it is waterproof.