Thank you to Fishtown for the pointer to another contribution. My S2218 had been without power for about 6 months. I think the main battery was completely empty. After the machine had received some charge it was able to run. It started with a default date. After a short run with network connection it received network time. The S2218 realtime clock was then correct. After a power down and restart the Date and TIme started correctly without any network update. Problem gone away! I think this means the Realtime clock is supported by the Main battery possibly indirectly via a rechargeable motherboard battery.
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