CMOS "Button cells"?
Button / Coin cells originally were ONLY Mercury types in 1930 when the clever package was invented by Mr Compton I think. Still available up to maybe the 1970s? The Silver types invented during WWII but rather expensive of course.
But Zinc Air, Alkaline, Silver Oxide and Lithium Button & Coin cells have been mercury free for over 20 years. Memory chips have been using Lithium or NiCd (then NiMH) type cells for about 30 years
I had thought Zinc Carbon/Zinc Chloride / Alkaline manganese batteries had always been mercury free (they are now), but apparently some mercury was used to help the Zinc Chloride material or something, which actually seems to be involved in all 3 mentioned Cell types.
LEDs can't come close to CFL for colour rendition (the wavelength is too long) a new LED material is needed. They also can't come close to power level of the higher power high pressure mercury vapour lamps.
Mercury based thermometers and blood pressure are long obsolete. The main issue is lighting.