In metal mechanical mods with bottom switches if the inside of the mod makes contact with the battery casing the mod will fire all the time. The whole battery casing is negative, so any time it is exposed there is some risk of it making contact with something it shouldn't.
This.
Right when i see a wrap starting to come up I fix, why risk it right.
Seen it go wrong on a friends 4nine and never wanted to have the same issue.
So yeah, always maintain them batteries.
Best friend or fire in pocket.