We want to remind everyone that taking care of your batteries is very important.  Taking care of your batteries will not only ensure safety but the longevity of use.  As we have stated in previous articles, Li-Ion batteries have protection circuits (click here to see that article on our blog).  The purpose of the protection circuit is to prevent from over or under discharge of the batteries and also short circuits.  Li-Ion batteries have a safe range of operation, which for a 3.7 volt battery would be roughly 3.0 to 4.4.  This varies a bit by manufacturer. But the protective circuit will trip if the limits of the safe range are reached.

In the protection circuit there is a wire that connects the positive terminal of the battery to the circuit board on the bottom.  The wire runs up the side of the battery and is insulated with a coating on the battery cell and the protective plastic sheath on the outside.  This protects from a short circuit which could cause the battery to discharge.  Generally a battery will not explode because it has vents on the top that allow the gases in the battery to be released reducing the pressure when the battery has a short circuit.  But keeping the wire protected is the key.  The outer sheath can become worn and can crack and rip over time.  If this happens you should discontinue use of the battery and dispose of it properly. 

If you are using a mod that is made of metal, the outer casing of the mod generally acts as the conductor of the negative terminal of the battery to complete the electric circuit.  So if your battery is damaged and the wire that runs up the battery is exposed and touches the side of the mod it can cause the protection circuit to trip giving the impression the battery is bad. 

If the insulation that prevents the wire on the outside of the battery from touching the cell is also damaged from misuse or wear and the wire touches the side of the battery, the protection circuit is bypassed causing a short circuit and that can cause the battery to vent.  Hence we are strong believers in taking care of your batteries and inspecting them for defects.  Just as a side note, dropping a Li-Ion battery can cause it to fail.  The solder point on the circuit board in the protection circuit can break from a hard fall onto a solid surface.

Below are some examples of batteries with the outer casing in various states of disrepair making them prone to failure and shorting.