I have quite a few new and used eGo and eGo-T 1100mAh batteries that amazingly still take and hold a charge, too. Like you, I also have my original cig-a-like JoyeTech 510 (a double starter kit) whose 2 batteries
still work, as do about 10 XL 380mAh additional ones I bought back in late 2013. Even have 2 brand new JoyeTech 510 double kits I bought in 2017, too...for nostalgia sake and if a friend ever wants to try switching to vaping with a cigalike!
My favorite mods in rotation for years have included the Innokin MVP2 and 20W, Eleaf iStick 20W mods and the Innokin Coolfire IV 40W mods. They just keep working...like the Energizer bunny. I've bought a

ton of newer mods & kits in a wide variety of types, wattages, etc., but nearly all are still NIB in the stash. I've got a file on my laptop & on a flash drive...of all of
them, as well as ones for the tanks, RBAs, coils, replacement glass, etc. in the stash.
As you said..."overkill creates a sense of security". I'm a firm believer in that, too. In my case, it's security for myself and for 6 other people. They've all got
their own liters of nic base in
their freezers though! There's no way I could stash all of it until they want/need it!