It has an internal component (I believe it is a capacitor ) that will retain date/time when the main battery is removed, but it is not user replaceable. Internal charge is maintained by main battery and will remain charged for a period of time when the main battery is removed.
John Hoffman
Conway, NH
R6 Mark III, M200, Many lenses, Pixma PRO-100, Pixma TR8620a, Lr Classic
