This is the best battery-backed real time clock (RTC) you can get that allows your Raspberry Pi project to keep track of time if the power is lost. Perfect for data-logging, clock-building, NTP servers, time-stamping, timers and alarms, etc. Equipped with a genuine DS3231 RTC, it works great with the Raspberry Pi and has native kernel support. This Real Time Clock (RTC) is the most precise you can get in a small, low power package. Most RTCs use an external 32kHz timing crystal that is used to keep time with low current draw. And that's all well and good, but those crystals have slight drift, particularly when the temperature changes (the temperature changes the oscillation frequency very very very slightly but it does add up!) This RTC is in a beefy package because the crystal is inside the chip! And right next to the integrated crystal is a temperature sensor. That sensor compensates for the frequency changes by adding or removing clock ticks so that the timekeeping stays on schedule. Item Specific Fully assembled & tested PCB plugs directly into your Pi's GPIO pins No soldering required Will keep time for 5 years or more Size: 21.3mm x 20.0mm x 13.6mm / 0.8" x 0.8" x 0.5" Weight: 2.7g / 0.1oz CR1220 coin cell battery not included