Holders for 18650 batteries. For balance charging or powering a load. Uses easly sourced parts. And is simple to print. Sketchup File included. 1, 2 and 4 tray holder. 4mm holes for M4 Hardware Springs : http://www.ebay.co.uk/itm/121197223478?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 Printed with: ColorFabb XT 260c 70c Bed (With Hairspray) 50% Fill 1.6mm Shell 45mm/s 15mm Brim This makes all walls linear travel fill, this stops silly vibrations trying to fill a small void and it speeds up print time. Uses standard red 4mm ring crimps. Links are made by stripping off Plastic two crimps and soldering end to end, see second picture.