Designed to use the freshly charged batteries in FIFO order. It is completely modular so you can create as long as possible by printing more than one middle items. To assemble the parts use an M4 threaded rod - I made holes for the hex nuts on the bottom parts. https://www.youmagine.com/designs/modular-fifo-aa-battery-holderPrint each part except top - there are two different "top" parts - you need only one of them, so make your choice. I made a short screencast about the design process in case you are curious: http://fns.csokolade.hu/2014/04/17/3d-nyomtatas-tervezzunk-fifo-elemtartot-aa-meretu-akksiknak/