So you spent 100 dollars on F-91W's over 30 years. 50 dollars could have gotten you a watch that would have lasted 30 years.
This is a lot of weight for a mass-produced, low-cost piece of consumer electronics to bear.
You're not counting new batteries.
It's true that you can buy a tool to change your own. But a small, rarely used tool is very hard to keep track of.