Unfortunately, your batteries have a hard life. Too hard even ...: Inserted and extracted from boxes or chargers, braving juice drips, but also falls, the batteries suffer greatly. And their external protective wrap can suffer and be damaged or torn. 

In this case, it is essential to act quickly to replace the wrap, which plays an active role in the safety of use, by protecting the body (negative pole), but also by maintaining the insulating washer present around the positive pole. Without this washer, the insertion or removal of a battery will certainly cause a short circuit between the two positive and negative poles and the battery will outgas. Hence the importance of a perfectly good wrap.

How to proceed?

1. Remove the old wrap from the battery without using metal tools 

In general, it is sufficient to pull on the edge or hook to tear off the plastic wrap and strip the battery. Avoid metal tools in the vicinity of the positive pole, especially if you have to make a small cut. Instead, use the negative pole for this operation. Take care to recover the insulating washer to put it back in place. If necessary, if the washer is in poor condition, do not hesitate to replace it.

2. Slide the battery into the new wrap 

The new wrap is a heat-shrinkable plastic tube, usually pre-cut to the right length. Simply press the edges to open it and slide the battery into it. Centre the battery in the wrap, leaving the same length on each pole, and make sure to put the insulating washer back on the positive pole.

3. Heat to shrink the wrap 

Simply apply a heat source (hair dryer, heat gun, or even a lighter flame) so that the wrap shrinks to fit the battery body. Start with the positive pole, the sheath will eventually fold over and hold the insulating washer; then clutch the whole body by turning the battery and end with the negative pole. Do not heat up the battery in one place, but rather move the heat source around the whole battery.

That's it ! Your battery is as good as new again and you can use it safely.