Charging an electric vehicle battery is an exothermic process, so the battery usually gets a little warm while charging. But sometimes it heats up abnormally during charging, which often shortens battery life. So why does an electric vehicle battery overheat? There are mainly two reasons:

1. Overheating caused by the battery itself, such as aging, increased internal resistance, dried-up electrolyte, or internal short circuits. As a battery is used more, through both discharging and charging, the water molecules inside it are gradually lost, which makes it heat up during the electrochemical reaction. In addition, the battery solution forms sulfate crystals during charge and discharge that settle and stick to the plates, increasing the battery resistance and causing heat. If the overheating is caused by a short circuit, the best solution is to replace the battery with a new one.

2. Overheating caused by the charger. A common charger has no pulse function, let alone a negative-pulse function to remove polarization, so this kind of charger usually cannot hold a constant voltage in the later stage of charging. As a result, the battery voltage exceeds the allowed value, causing heavy gassing, water loss, and heat. A slight amount of heat is normal, but if the heating is abnormal while the battery is in good condition, the charger is the cause.

In addition, always follow the manufacturer instructions during charging, especially the charging time. A longer charge does not mean greater capacity; charging too long may damage the battery or even cause a fire, while charging too little and cycling frequently also does real harm to the battery.