DS3231

ds3231frontds3231back Description real time clock module
I have paid $0.62 / piece (free shipping)
Interface I2C
Dimensions board size: 22 x 38 mm, 3 x mounting hole M2
Datasheet ds3231.pdf
Library Arduino: ds3231.ino (test code), Timezone
Other Use rechargeable battery LIR2032. You must cut off charging circuit (diode + resistor “201”) in order to use common CR2032 battery.

References

ZS-042 DS3231 RTC module (forum.arduino.cc)