need help with mod idea.

I hjave this old otoscope that I had in my aid from when I was in the army. really wanna make it into maybe a 5v vaporizer to use 801 atty's. problem is the Twist type on/off switch it has how do i get around this and use a push button. the black ring on top is the on/off ring.

 

It hard to tell how big it is or how far the batteries go up in the tube from the pictures.

Positive:
If it was mine and the batteries went all the way to the top inside of the case.

Make a small disk from plastic and add a small spring (DO NOT LET THIS TOUCH THE CASE // Positive + Negative = BAD). Might be better to use a small washer or something you know won't touch the side and let the bottom spring do the pushing. The reasoning behind this disk is so you can recess the batteries to make room the top for a switch etc.

Drill a hole in the disk, run your + lead wire from the spring etc. out of the hole coming out the back of the disk.
Then put in your batteries and the bottom cap, then the disk on top.
JB weld the disk. Wait for the weld to dry.
Then Stretch out the spring to make it a tight fit. I guessing that black piece on the top is metal, so you'll have a good negative connection.

Drill out the top to fit which atty you want. Outside is negative so run ur + wire from the disk to the center of the atty. A little JB weld and your set.
(Tip: Get your finger wet, and you can mold JB weld to make it smooth)

I would highly suggest drilling out ventilation holes. CR2's can explode. I would suggest the bottom and a couple on the side where your hand isn't going to be most of the time.

I've made a device called the black & decker mod that used this disk method I'm explaining if you want to check it out. Scroll down for the diagram:

http://www.vape.to/forum/showthread.php?1138-My-Black-Decker-Battery-mod-(in-progress)