Okay, keeping a pack of alkaline batteries in the fridge, no problem, right? Well, e-cig batteries aren't just batteries, there's sensors and microchips in the "battery" housing that can be damaged by the condensation when you take it out of the fridge. I don't know about you but I really wouldn't want to test how hard it is to cause a short with a lithium ion battery and some water!
Just keeping e-cig batteries in a drawer in your house is good enough. I wouldn't keep them in my glove compartment in my car for instance, since vehicles tend to go through an extreme in temperatures, and even places like garages do too.
The li-ion batteries normally have an insanely low self-disharge rate. However, depending on the type of automatic sensor an e-cig battery might be on standby, listening and waiting if it's one of the types that use a microphone to sense "inhalation noise". If it was completely powered off, how could it monitor for sound? So, the battery must maintain a "trickle" charge to the circuitry, and eventually drains the battery. In normal use, the battery is prevented from being deeply discharged.When stored for long periods, however, the small current drawn by the protection circuitry may drain the battery below the protection circuit's lower limit, in which case normal chargers are unable to recharge the battery. More sophisticated battery analyzers can recharge deeply discharged cells by slow-charging them. Even with a manual switch (no "stand-by" sensor) on the 510 batteries this issue exists, just wanted to point that out.
Due to the nature of li-ion batteries, it really makes no sense to buy e-cig batteries to stock up, because invariably, you will lose up to 20% battery capacity a year, just sitting there. The reason you want to store li-ion batteries long term at 40% is because it slows the self-discharge rate a lot, it's an industry standard, and that is why most e-cig manufacturers ship their e-cig batts charged at about 40%.