The DS1307 serial real-time clock is a low power, small packaged yet powerful calendar. Data is transferred in Serial via I2C. The clock is capable of providing seconds, minutes, hours, day, date, month, and year data. The clock operates in either the 24-hour or 12- hour format with AM/PM indicator. In addition, the end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The DS1307 has a built-in power-sense circuit that detects power failures and automatically switches to the backup power supply. It uses CR1220 battery and which is NOT Included. It is great to use with your Arduino-related projects!
The battery is Not included.