Many people have noticed that the shell of an electric vehicle battery becomes very hot during charging, yet most consider it normal. A battery is allowed to warm slightly during use or charging, but abnormal heating is not allowed. If the shell feels clearly hot to the hand, the battery is heating abnormally. In this case you must not ignore it, because abnormal heat does great harm.

Heat first evaporates the electrolyte moisture and gradually dries it up, then lowers charging efficiency, deforms plates, increases internal resistance, accelerates oxidation of mechanical parts and can burn plates or separators. In the end the capacity drops and the life shortens. So if you find abnormal heat during use or charging, never ignore it.

Battery heating falls into two situations: one is heating during discharge, that is abnormal heat while the battery is in use; the other is heating during charging. The causes of abnormal heating differ in different situations.

1. Causes of heating during discharge: discharging too fast. The battery capacity may be small while the discharge current exceeds 0.5C for a long time. It should be emphasized here: after a short trip, although the battery consumes some power, after resting it recovers and the electrochemical process of the plates continues, so the voltage rises again, but this does not mean the capacity recovers. On the contrary, on a long trip without stops, the electrochemical action of the plates and the consumption of power proceed at the same time, and three situations may occur:

(1) When the rated motor voltage is low, the battery capacity small and the working current high, the voltage drops sharply and the capacity is quickly exhausted, which is the most unfavorable to the battery.

(2) The electrochemical reaction speed of the battery can barely sustain the ride, the battery has no chance to recover and rest, and full charge-discharge cycles are frequent, so over-consumption happens easily. Facing headwinds and uphill sections, power consumption is great and the plates are forced to react violently, so the shell runs hot, the battery is damaged, the life shortens, and the capacity is not ample either.

(3) Ideally, the electrochemical reaction speed of the battery can comfortably supply enough power. If the shell shows no abnormal heat, the battery capacity is ample.

Of the three situations, only the last one is ideal for long-distance riding. It should be noted that if the shell feels clearly hot, the cells inside are even hotter.

2. Causes of heating during charging: while a storage battery is charging, part of the electric energy converts to chemical energy and part to heat and other energy. Warmth during charging is normal, but when the temperature is high, check in time whether the charging current is too large or whether an internal short circuit has occurred.

The amount of heat has little relation with the amount of electrolyte. In sealed batteries with little electrolyte the internal resistance grows, which also raises the temperature, and the terminal voltage becomes very high during charging. Battery aging, dried electrolyte and internal short circuits can also cause heating. If the charger cannot work in constant voltage in the late charging stage, the battery voltage exceeds the permitted value and the temperature rises; in severe cases the battery swells and its life ends.

In use, try not to place the battery sideways or upside down, so that gas generated in large amount at any moment can be vented smoothly through the valve, especially during charging; otherwise the shell may burst.

In short, whenever abnormal heat appears, never ignore it. Take the battery to a professional maintenance shop for service as early as possible.