ramussons the capacitor idea is intriguing. How long of a power outage do you think that setup might keep the clock going for?
Ok thanks to everyone for cluing me in on the Schottky diodes. I went ahead and ordered some 1N5817 diodes, hopefully those would be a sufficient type for this application.
In the meantime, I decided to do a little experiment. I connected an alkaline AA battery in parallel with the output of the buck converter, which is also connected to the clock battery contacts. Before doing this I measured the battery voltage and it was exactly 1.487 volts. I also measured the output of the buck converter which was powering the clock and it came in at 1.6 volts. I figured this was close enough and maybe it would even charge up the battery a little bit.
After connecting the battery in parallel I came back after about 30 minutes to find something very surprising. I connected my meter to everything and to my astonishment it read 1.95 volts. I didn't expect anything above 1.6 volts. So then I disconnected the battery and measured it. It was at 1.73 volts and gradually decreasing. The buck converter still measured 1.6 volts with the battery disconnected.
I went back and measured the battery again after a few hours and it stabilized at 1.567 volts.
Something strange was happening when I had the battery connected in parallel without any diodes. When the diodes get here, I'll try putting them in so that no electricity can flow from the buck converter to the battery and so no electricity can flow from the battery to the buck converter.
Just thought that was very strange how the voltage increased to more than either of the power supply sources when in parallel....