This 5/2 day programmable 'stat has worked great for at least 10 years. TheLCD readout is a bit fuzzy, but otherwise seems to function just fine. I noticed a "Battery" flashing as I adjusted the time, and this was the first time I saw that. I think it is "hard-wired" on the wall. Where is (and what kind of) the battery I need and How to replace it? Thanks for any help.