Here's another one... how often do you guys have them inspected and tested? Coming from three generations of fire fighters and fire inspectors, I bought a half dozen good (not Kidde crap) fire extinguishers from the local company that supplies all of our fire co's, and added them to the few I had already inherited... all in 1998. They are still showing exactly the same charge they started with, or very nearly so, on their gauges. Assuming the gauges still work, that is.
Not a great practice, but since it's now more than an hour round trip to where they're serviced, and I'd not want to be without more than one or two of them at a time, I haven't found a great solution for getting them tested and serviced.
Oh, and the few I inherited? There's two Halon's in that group! I also have the same water extinguisher Hay Dude carries on his tractor, I use it while welding. Do be sure to check the charge on those frequently, as mineral deposits can cause slow leaks on those.