I made a battery saver for one of my vernier calipers using an AAA battery

https://www.instructables.com/preview/E2VL1TBJGGTD...

It works perfectly but having found a slide switch that was smaller than the one I used before and, as I had yet another battery eating vernier needing modification, I thought I would redesign the whole thing :). I decided to stick with the standard battery as it lasts ok on a vernier that doesn't drain it when switched off.

No disassembly of the caliper is required to do this mod, just removal of covers.

Step 1: Parts and Tools

Not many parts or tools required for this build:

Parts

Vernier caliper with battery
6mm perspex
1mm brass
3 M3 Dia x 4 csnk screws
Small offcuts of .5mm brass for contacts
50mm of thin insulated wire
JB weld adhesive

Tools

power drill (pistol or bench) & drill bits
hand files
soldering iron and solder
Needle drill chuck
M3 tap

Step 2: Fitting the Switch

The switch fits in the recess where the battery usually sits, make room for it by carefully cutting out the plastic at the end to the width of the switch.

At this point confirm which terminal is attached to the frame of the vernier, in this case it is the positive so the switch will attach to the negative. Carefully bend and cut off the sprung parts of the battery contacts and tin what is left of the negative (the square one in the middle) .

Bend the centre and one end contact of the switch at 90 degrees, join them together by soldering a piece of tinned wire across them. solder a piece of thin insulated wire to the third terminal.

Now hold the switch in place and solder the joined contacts to the negative pad inside the battery compartment.

Take off the little side cover for ease of access, and using a drill just over the size of the piece of wire enlarge the existing hole on the corner of the battery holder, thread the wire through and replace the covers.

Step 3: Battery Holder

The 6mm perspex was cut to the width of the metal backplate of the vernier, the length is unimportant it just needs to have room for fixings and the battery. The cover was cut to the same size from 1mm brass.

Step 4: Attach the Battery Holder

Remove the aluminium foil label from the back of the vernier and clean off the glue, I scraped it off with a sharp chisel.

The holder is attached to the vernier with JB weld, make sure not to let it spill into the battery holder hole as this will cause problems with contact later. Make sure you pass the wire through the angled hole before pressing the parts together. Leave for 24 hrs to harden off.

Step 5: Connect It Up

I cut a couple of small pieces of thin brass one of which goes under the battery, the other one fits the part drilled hole, I gave it a thick blob of solder before connecting the wire as I wanted to be sure it stood proud of the perspex, I tickled it up with a flat file to get it just above the surface so that it would make good contact with the back cover.

Step 6: Cover on and Test!

All that remained was to screw the back cover on and test.

My first fixed vernier sits on the surface plate in the workshop, this one sits beside me at the computer both are always ready to use every time I need them.