This RTC module is specifically designed for the Raspberry Pi. It communicates with Raspberry Pi through I2C bus and includes a Maxim DS1307 and CR1220 button cell on the board to keep a real time clock for a long time after the Pi has powered down. Just set a serial port, and you have a convenient way of online debugging using TTL. Supports Raspberry Pi B/A+/B+/2 model B/3 model B/Raspberry Pi 4B.

• RTC module: DS1307
• Battery model: CR1220 button cell
• Operting Voltage: 5V
• I2C address: 0x68
• Clock precision: ±2ppm (0~40°C)
• Unit information: Second, Minute, Date, Week, Month and Year
• Operating temperature: -10°C ~ +85°C
• Compatible with Raspberry Pi B/A+/B+/2 model B/3 model B/Raspberry Pi 4B
• Interface: 2*5p 2.54mm

• Wiki Doc 

• RTC module with Battery for Raspberry Pi x1
• DS1307 Button cell x1