For occasional use like that you want low self discharge NiMH. Sanyo Eneloop, Rayovac Hybrid, Maha Imedion, etc. I use those with all my gear, one set in the camera, gps, etc, the other ready to go.
I would try with a set of them in and see if it still drains, sometimes drain is caused by the batteries internal resistance rather than the device itsself.
Also remember a decent charger, most of the ones you find in box stores are crap, the powerex maha, or lacross are the best.
Between the wife and kids and I we have 4 digicams, two GPSs, two way radios, and various other battery powered toys. I use eneloops in all the primary gear such as our GPS's, scanner, etc and the maha in the kids cameras and good toys, nintendo wii remotes, etc (the maha seem to be just as good as eneloop, I just use the black and white batteries to tell them apart.
I have two chargers, a maha c401fs and a maha c9000. About once a year I'll run a test on the batteries with the refresh cycle on the c9000 to see how they are holding up.