Replaces a Dallas DS12887 Real-Time-Clock chip, and provides user-replaceable battery so you don't have to replace the entire chip when it runs out. Uses a common CR1632 cell, found in supermarkets and dollar stores. Battery is NOT included due to shipping regulations. Watch orientation when installing. The chip has a notch at the Pin-1 end. Can almost always replace the older DS1287 as well, but some systems are picky. DS12887+ is just RoHS-compliant DS12887, and this can replace that too.