This is one reason I prefer "user" kits rather than emergency only kits. Kits with expendables (batteries, MRE's, water, et al) need to be used and expendables replaced with new as they are used. It keeps everything up-to-date.
To me, that is the key to easy maintenance of your kits. they do not sit unnoticed until you need them, you use them, and all of the equipment in them on a regular basis. All of your equipment and supplies get rotated and maintained constantly. It is more difficult if you are not in a position where you have opportunities to use the stuff, though. I am fortunate in that way. All of my electronics, knives, tools, supplies and other stuff get practiced with and used, in my work and with the scouts. I try to teach this to the scouts (and their parents).