The battery power module is finally finished. I initially intended to use a half-AA lithium cell but it turns out all but the most expensive variants are only suitable for very low current applications and cannot provide anywhere near the sustained current required for the pico-mac-nano. I ended up using the larger C2 lithium battery which was a real challenge to fit in the case with contacts, voltage regulator and microswitch, and requires some fiddly wiring.

I'm pretty happy with the result which incorporates a rocket for the switch that appears on the rear of the case.