Had an issue like that with one of mine, what I figured ot was the o-ring seal doesnt quite "seal" I put some silicone grease on it after it dried out and bang problem solved. I have several of them and have only had the issue with one so far...but YMMV....
Went with saba slayers reccommendation and sourced some replacement batteries online for much cheaper:
http://www.amazon.com/Maxell-LR44-Ba...r-44+batteries
I also have the light from wallyworld that GR6RR mentioned, haven't tried it out yet but seems even less waterproof, will test it out next trip and see how it does.