The good thing with my current bike is that it never runs out of fuel, by design. I can pick it up anytime and it just works, it was so 10 years ago when I acquired it, and it'll be so 10 years down the road.
I have a Garmin Forerunner 735XT watch and it needs charging every 15 days, which is better than any "true" smartwatch out there. At some point in the distant-but-not-so-much future the battery will flat out die and there will be no replacement part. The experience from my mechanical watch is entirely different: it keeps on ticking as I move around, and the thing will probably end up surviving me.
Going from zero to non-zero - whatever the value of non-zero is - is non-negligible mental weight. Zero is a freeing experience.
Although with 20 years of use, those gear cables are likely to fail. Presumably you do things like lube the chain, inspect your tyres, keep them inflated to the correct level?
I've had a couple of Di2 batteries fail. One of them went suddenly and I had to grab a train to get home. The other one lost capacity quite quickly, so I'd have to charge it once a week until it got so bad I needed to charge it fully each day until I swapped in a new one.
This would be like someone running out of fuel in a car. A known limitation which is completely avoidable.