I've sort of standardized too. I basically always have two of something, two knives, a spare key and normal key, whatever so I settled on two types of batteries. Currently I've standardized to AAA and AA and the majority of my gear all fits this standard except for a couple things like smoke detectors that take 9v or the key fob that takes tose tiny lithuim batteries and cell phone which takes its own. This makes it easy to keep plenty of spares in stock, don't have to buy a bunch of different types, just buy a bulk pack of one or two types.