I just loosen the atomizer a couple of turns to break contact and then power off the mod. If you are concerned about something happening just set it in a metal pan for the night. There's no history that I've read about idle mods suddenly spewing a battery.
Usually any issues are traced to under rated batteries or something causing a direct short INSIDE the case. One case was a Snow Wolf with a magnetic battery cover that came off in a guy's pocket where he also had his key ring. Keys got across the battery and welded. He got a nasty burn while trying to remove his pants.
The moral of that story is replace it if it's broken, keep it where you can toss it, and don't put it in a pocket with other metal items.