I've been working on adapting a Ryobi 18V Lithium battery to replace the batteries in an old respirator. This is a big process and along the way I've created the sub-assembly for the Ryobi battery which snaps on just like the Ryobi tools.
It prints in two pieces that are attached using cable ties, this allows the print surfaces to work on extrusion printers, like the PrintrBot Simple Metal (which the above was printed on). The cable ties do an amazing job holding it all together, I though I'd need to do a plastic weld in addition, but they are held just right.
The metal clips are AAA battery snap on clips that match the power supply perfectly. I found them at Amazon by searching for "AAA N snap-on clip" and found them from www.mouser.com (part #534-204).
My next stop will be the attachment to the respirator, but in the meantime, you can modify to start printing your own tools!
The design allows for the printer to extrude a bit of extra on the edges (as my printer does). This way the fit isn't too tight. In general I've allowed an extra 0.5mm around the edges.
When the two pieces are printed, attach with some small cable ties. The holes are 2mm x 4mm which accommodates the 1.5mm x 3.5mm cable ties that I used.
Make sure that the head of the cable tie is on the "top" of the model as there isn't enough room between the model and the battery.
The clips simply push down and onto the printed grooves.