Because of the recent tensions with NK, I opened up my RADEF ammo can to check on my radiation meters. Yes, I know, they are from the Cold War (Civil Defense Issue) and probably aren't close to being calibrated anymore. But hey, it's what I've got for now. I never store items with batteries installed. However, the alkaline "D" cells had disintegrated into powder; they were from 2009. Luckily they were double bagged and didn't damage anything. The 22 1/2 volt carbon batteries (now obsolete) were intact, but dead. One meter takes a single "D" cell. The other two each take a "D" and two 22 1/2 volt cells. I can get new manufacture alkaline 22 1/2 volt cells for about 10 bucks each; cheaper than making up packs with 9 volt batteries in series.
Given their age ,although carefully stored and in good condition and dubious reliability, I'm not sure if I want to drop the 40 bucks to have batteries for them. I should just bite the bullet and buy a new, proven unit. So, don't store anything electronic with batteries installed.