Really not are need one 3 years clock without power, only one capacitor with maintain date and time for 10 minutes, or just for reboot…
And is better than start date/time with RouterOS build date and time.
For example, if the package are made 26/06/2014, is absurd to start the clock on 1970…
Or better, if the bios [firmware] are builded for example 25/05/2014 is absurd to start the RB with one previous date…