The RTC Plug is a small board containing a low power real-time clock with battery backup, which continues to track the time while external power is switched off. The battery life is good for some 2-3 years on real-time clocks as the battery only keeps the clock chip oscillating when the board is powered down.

An I2C bus running at 3.3V is used as interconnect, with all the power and signal lines brought out to to both sides of the board to allow daisy-chaining with other I2C-conformant boards.

The pre-assembled version comes with the SMD-sized DS1340 chip, crystal, battery holder, and decoupling capacitor already soldered onto the board, CR1220 battery and 1 1x6 right-angle male header.

The PCB only variant contains just the board for the RTC Plug. No parts, no headers, no battery.