You just accidentally activated a dead battery. The special point of the lead battery is that his two plates are made of lead, stored on the electricity, the positive plate becomes lead dioxide, the negative pole is still lead. After the telex release, the positive and negative electrodes are turned into lead sulfate.
The basic two plates of your scrapped battery have become lead sulfate crystals, reverse charging activates lead sulfate because of the different plate structure, and then forward charging is smoothly filled in. However, reverse charging is dangerous, and it is easy to cause the active substance to fall off and make the battery completely scrapped