
I received 4 RTC modules, two with the more accurate SN version of the DS3231 chip as shown in their pictures and 2 were the M Version with lower precision chip. As far as I remember the description doesn't specify the type but the photos show the SN model so I thought I was sure. not so. I returned 4 RTCs and bought the same RTCs from another seller (different Amazon product display but identical product) and received 4 RTCs with SN chip. Another thing to check is the battery voltage as I don't think they are rechargeable. and one of the RTCs had a slightly dead battery. I probably wouldn't if that was the only problem, but 2 cheaper chips with lower accuracy wasn't acceptable. The product came with no instructions but they are pretty easy to find online. When I received a new kit from another vendor, it took me a few minutes to set it up on my 3 RPI 4 running Raspbian Buster lite.

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