Random recommendation.
I’ve used a maxim ds1307 in the past, for providing fairly accurate time to an arduino or a raspberry pi that isn’t on a network. I feel like they’re delicate. I’ve had two fail for no obvious reason. In both cases I suspect the crystal they use for keeping time got damaged. So I ordered another, and what they shipped was a ds1302: the same chip with an SPI interface. Man, there isn’t a lot of stuff out there for SPI peripherals on the pi, and I didn’t want to write my own. I was just SURE I had another chip/module around somewhere, so I kept looking, and found a DS3231, which has the clock crystal internal to the chip package. The thing had been rattling around in a gym bag for three years, and when I powered it up, it was less than 12 seconds off the actual time. AND it provides a hardware clock output in addition to the digital interface. It costs more than the 1302, but I’m happy with it.
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