During the charging process, part of the electrical energy is converted into chemical energy, and a part is converted into thermal energy and other energy. It is normal for the rechargeable battery to heat up. However, if the temperature is high, it should be checked whether the charging current is too large or a short circuit inside the battery. The heat generation has a small relationship with the electrolyte volume. If the amount of electrolyte in the sealed battery is small, the internal resistance increases. Large, it will also cause the battery to heat up and the terminal voltage is high when charging. Battery aging, electrolyte drying, and internal short circuits can also cause heat. The charger can not be at a constant voltage in the later stage of charging, so that the battery voltage exceeds the allowable value, the temperature will rise, severe swelling, and the end of life.
In use, try not to lie horizontally or reversely, to prevent a large amount of gas produced inside the battery from being discharged smoothly from the venting valve, especially during charging, otherwise the casing may burst.