I was hoping someone could school me on the TAC20 and TAC32 main controller board batteries. What they actually do, how often to change them, the procedure for changing them, are they changed with the power on or off, ect. I know the DMC control board battery located in the COP is termed the clc backup battery and is changed with the power on, if not you'll lose all of your saved parameters and get a cold start fault. I've heard stories of guys putting tape on the backside of the clc battery after losing a contract to competitors. I was told years ago as a young service/repair mechanic working for Thyssen Sound Elevator that the DMC clc battery should be changed once a year. I seem to be ok changing them every two years. I appreciate any insight. Thank you