BUY DS1688S https://www.utsource.net/itm/p/169830.html
3 Volt/5 Volt Serialized Real-Time Clock with NV RAM Control
Description: The DS1688 is a low-power, real-time clock/calendar with 56 bytes of battery-backed nonvolatile RAM. Features: Real-time clock/calendar with 56 bytes of battery-backed nonvolatile RAM Low-power operation Multiple time-of-day alarm settings Programmable square-wave output Programmable interrupt output Automatic power-fail detect and switchover Automatic leap-year compensation I2C/SMBus compatible Applications: Automotive Industrial control Medical equipment Networking/telecommunications Security systems White goods (For reference only)