Why only a year on mechs? I have a ton of mechs, but I don't expect many of them will be rendered unuseable in the near future.
Just curious....
I needed to put a number in there for how many I could possibly need. I don't use mech on a regular basis. Only tested the ones I have for a short time. I am just playing odds on big numbers with limited knowledge as a backyard mechanic. I do know that things wear out.
Replace battery twice a day= 730 time a year
Replace topper twice a day=730 times a year
Fire device on average 500 times a day =182500
Thats the numbers I worked out for my stash.