If you are using a Raspberry Pi and if you need the keep the time even if there’s a loss of power and if you have no other means of getting the actual time (through the network maybe) then you need a real-time-clock.
RTCs need a battery . The batteries live long (2 years or so) but when they die, they typically die at an awkward time (ha!).
Mine died today – again. I am using the PiFace Real Time Clock . No chance of getting that particular battery (CR1220) on a Sunday. Also I wanted a battery that lasts longer. A so called “bettery”.
So I improvsed.
I found an old plastic case with a battery compartment. There’s not much more to say, the pictures tell the story. Ugly, but fits my use case. Works well.