To keep the price low, Raspberry Pi does not have Real Time Clock (RTC) hardware (see 'Why is there no real time clock (RTC)?' from the official FAQ). This is not a problem if your Pi is always connected to the Internet as it will synchronize the time with NTP (Network Time Protocol) Servers.
However, the Pi does not keep track of time during reboots and when it is powered off. If it is not connected to the Internet, it can't synchronize with NTP and you will notice that the time drifted significantly. This could be a problem if your project depends on time accuracy. To maintain accurate timekeeping, a dedicated RTC module can be used. The module has a battery to keep track of time even when your Pi is not powered up.
About this module
This RTC module is specifically made for Raspberry Pi. It communicates via I2C. The header socket is fully assembled. This module plugs directly to GPIO header (see the detailed image in the gallery). There are 5 unused pins (power and UART) extended on top so that you use it for other purpose. This module is powered by a CR1220 removable coin cell battery.
This RTC module is compatible with RTC-DS1307 Linux driver. It is installed by default in Raspbian, so there is no additional device driver needed.
This product is compatible with all Raspberry Pi models.
Features:
IC: Maxim DS1307
Interface: I2C
Powered by a CR1220 removable coin cell battery (included) during power off cycles
Specifically made for Raspberry Pi, just plug the module to GPIO headers
Board dimension: 22 mm x 26 mm
We have another RTC module for Raspberry Pi with higher accuracy DS3231 chip and smaller but comes with non-removable battery.
