Have you tried rechargeable batteries NiMH something in the 2450 mAh range should give you longer life and over time cost you less to operate . Get a proper charger for it , the whole kit will be expensive but will definitely pay for itself over time
http://www.amazon.ca/s/?ie=UTF8&keywords=amazon+aa+rechargeable&tag=googcana-20&index=aps&hvadid=74514751854&hvpos=1t1&hvexid=&hvnetw=g&hvrand=7323503829431598030&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_1b6ynykuxw_b
Just to show you what I mean , The higher the mAh the longer they will last between charges. Hope this helps