When taking your phone to some shop, there is a good chance that you will end up with a different battery. This is how they swap them.
Since you have boldly labelled your battery with a name or sign so that you can know it at a glance, that outer cover is carefully peeled with the aid of benzene, a chemical commonly known as dryclean.
It’s then transferred to the bad battery which has also been peeled so that it retains the labels you put on the original good battery. Whatever the case, find another way to protect your valuable battery, but think twice before giving it out for charge.