Get some IMR batteries for it..
http://www.supertmanufacturing.com/batteries.html#aw these limn batteries hold a charge a-lot better than li-ion and they're safer to mess with
I don't know what that thing uses, but if it takes four AA try two 14500 IMR batteries and two dummy batteries... you'll be over volted a bit but I bet it'll be okay.. The 14500 are 3.7v vs regular AA batteries at 1.5v .. Get those and the thing will run all day