I got the round adjustable one from heartfelt. Calibrated it and now have it set. I'm real happy with it so far. I want to mount it to my humidor lid with the adhesive back but my question is, how often does the battery need to be replaced? The instructions say the hygrometer refreshes every 10 seconds. I don't want to "stick" it in there and then have to pull it out in a couple of months. What do you all think?