There's your problem, you're using rechargeable energizers.
Look through here... http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.XRC+5+cell+hump+pack+battery.TRS0&_nkw=RC+5+cell+hump+pack+battery&_sacat=0
Find the one that fits your budget. They do NOT slip...