Video on the water battery that supplies power for decades. Cant seem to upload it here, can be watched at https://youtu.be/pjUUYSgTEsY (https://youtu.be/pjUUYSgTEsY)
For the same money you can buy some Lithium batteries which will also power a clock for 10 or 20 years.
I have a pocket calculator which is almost 30 years old and it's still running on the same Li battery.
I have a TI-108 calculator been running many years. I took it apart one day to clean it as drink spelt on the keys. Know what I found, it has no battery in it. Just a solar panel on front, and a capacitor in place of where I assume the battery would be. Works with any room lighting. Which makes sense really who needs calculators with batteries that quit working when the battery drains. After all no one is going to use the calculator in the dark anyway.