i had the same problem with mine when i started found out that cheap c cell batteries dont last more than about 4-5 days the weaker they get
the less the flash brightness is.

what i did was converted mine to use a 6 volt battery that goes in those battery powered cars for kids.

here is the proccess 8 inches of speaker wire soldered ends to the pos. and neg. termanals inside the camera then drill a hole in the case ( not the door of the camera) just big enough to get thewire through tothe outside put termanals on the ends of the wire and connect to the battery use silicone to seal the hole in the case.

this battery last about 3 months

here some pics from mine