The positive side denting is the most likely scenario for failure in a seemingly safe setup, and almost inevitable on an iffy one. Most see a protruding 510 and think it is safe, but denting the positive side of the battery is not difficult. I saw it happen using my SMPL. If your 510 pin is borderline, it will soon dent enough to allow the positive contact to touch the threads. It is a safe bet there are plenty unreported occurrences. I retired my SMPL to be used only if absolutely necessary, just isn't worth the risk
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Denting of the top of the battery is something hardly ever mentioned with this problem.
Somebody might have an atty which has a center pin that protrudes 1/2 mm, and they think that's good enough, and it seems to work fine one minute, then they switch out to another battery, but the replacement battery has become indented with use and especially from being hard-compressed inside a mech mod instead of being housed with a spring-compression flashlight type housing; at this point the battery gets shorted out.
A real hybrid atty has a BIG center pin which sticks out more like a half centimetre from the base of the atty, not a half millimetre from the bottom of the 510 thread of the typical atty. With a BIG center pin there's also no chance of denting the battery.
Issues around these types of mods with no center pin:
1: Require an atty that has an extended center pin.
2: The small 510 atty center pin might dent the top of the battery and lead to a short
3: An atty might have a center pin which looks like it sticks out a lot, but when you scew it down, the centerpin might get pushed up! and the 510 thread ends up in contact with the battery causing a short. Some attys even have a spring loaded center pin.