Bulldog clip with one side insulated? Just for testing perhaps but could also be retained if you want that "throwie" feel to the assembly.

Hi Paul,

Coin cells have high internal resistance.  Putting them in series only makes matters worse.  

I suggest you to try first if that pile can power your circuitry.  You could quickly make a pile using scotch tape.

Good point. My stuff will run on 3V. Some needs to run on 3-5V, but the HV parts will be more efficient with a higher input voltage. Of course, the other reason for four cells is to have more mAh, which could also be done wired in parallel, then I wouldn't get the added efficiency from a higher input voltage.

What about just drilling a hole of the right size. Drill a small hole from the side to the bottom to place a stripped wire as one terminal. Or drop a small piece of PCB down there with a thin wire soldered on. You can screw the top of the hole shut with a piece of metal or PCB as the upper terminal.

Extra points for adding a spring somewhere. But you can also just make the hole a bit less deep than the stack of batteries and then clamp them with the lid.

I've used a tube before, it depends on your orientation I guess:

https://hackaday.io/project/27580-global-view/log/74559-holding-and-shipping