tack:
It's not just the power source you have a problem with, it's the whole device. There is no hard and fast data to prove that any electronics will actually last that long. At the very least you'd need some kind of hermetically sealed container to have a good chance of working preservation, IF you had confidence in a reliable power source.The chances are that one of the crucial link components will fail way before that 100 year period is up.
Without some form of regular check and maintenance, I'm doubtful you'd get anywhere near the longevity you require.
I'm not so sceptical about the electronic components not lasting that long if the power source life can be solved.
At the refinery I worked at before retirement we still had some equipment at or more then 40 years old that had semiconductor components (diodes, SCRs, transistors, etc) still operational, so I don't think 100 years life output of semiconductors is a automatic show stopper. Especially if it's in some kind of 'sleep' mode that only wakes up say once day or week or month to check the date and then goes back to sleep if 100 years has not elapsed.
Lefty