Was it store bought? You never know if it was used as a demonstrator, or how long it's been on prior to your buying it (some one might have forgot to turn it off after looking at it?). I suggest replacing the battery and then keeping an eye on it.
perhaps the heat from firing your gun? dunno, but my eotech likes to eat batteries and it sucks. maybe its time for an Aimpoint.I can't say heat is the problem, its been a mild summer here & I keep the gun indoors except for shooting. What do they use in the deseart? Lithium? Buy the way tzoid good shooting!