Our RTC breakout is based on DS1307 clock IC which supports the I2C protocol. It uses a Lithium cell battery (CR2032). The clock/calendar provides seconds, minutes, hours, day, date,month, and year information. The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator.
Along with time, the breakout can be used to get a nice square wave output either 1Hz, 4.096 kHz, 8.192 kHz or 32.768 kHz from the dedicated pin.