Answer: The reasons for the battery charging heat are:
During the charging process of the battery, part of the electrical energy is converted into chemical energy, and part of the electrical energy is also converted into thermal energy and other energy. It is normal for the rechargeable battery to heat up, but when the temperature is high, you should check whether the charging current is too large or a short circuit occurs inside the battery.
The relationship between the amount of heat generated and the amount of electrolyte is small. If the sealed battery has a small amount of electrolyte, the internal resistance increases, which will also cause the battery to heat up and the terminal voltage to be high during charging. Battery aging, dry electrolyte, and internal short circuits can also cause heat. The charger can not be constant voltage in the late stage of charging, so that the battery voltage exceeds the allowable value, the temperature will rise, it will swell seriously, and the end of life.
During use, try not to place it horizontally or upside down, to prevent a large amount of gas produced inside the battery from being discharged from the air release valve, especially when charging, otherwise it may cause the casing to burst.