Before ordering the boards from OSHPark I wanted to do some "fit testing" with a paper prototype (basically just a printout of the board render in 1:1 scale and cut out with an x-acto knife). Here are some pictures of it in different kinds of battery holders:

AA holder of a wiimote:

AAA Holder in a Pokemon Mini console:

This one really shows the usefulness of the flexible pcb, as the battery terminal is recessed into the plastic, so the board needs to bend to reach, here is a picture of the console without the battery:

It will also even work for many button cell holders!: