I forgot mine on, maybe setting 3 or 4, for about a week once. Other than that it has been turned on a half hour at a time, probably once a month on average, for about three years now. Still going strong.
I'd guess that the factory got a hold of a bad battery. Even new off-the-shelf batteries can be junk.
The last nice flashlight that I bought I almost returned due to bad battery life. It came without batteries, but I put a brand new, name brand, recently purchased locally, cr123 in it and it was dead in no time. I never even used the high settings. The other battery in the package, same thing, dead in a few days. So now I am disappointed enough in my expensive flashlight to write a negative review on Amazon.
However, I eventually got around to buying some more batteries and giving it another go. These ones last for months. I had to go back and change my product review.