Perhaps many people will find a situation where the battery casing  of an electric vehicle is very hot when charging. However, many people believe  that this is a very normal thing. The battery is allowed to generate small heat  during use or charging, but abnormal heat is not allowed. When you touch the  battery casing with your hand, you can clearly feel that it is very hot, which  indicates abnormal heating of the battery. In this situation, everyone must not  ignore it, as the harm of abnormal battery heating is  significant.

Heating will first cause the electrolyte moisture to evaporate and  gradually dry up, followed by a decrease in charging efficiency, deformation of  the electrode plate, an increase in internal resistance, accelerated oxidation  of mechanical components, burning of the electrode plate or isolation material,  and finally manifested in a decrease in battery capacity and shortened lifespan.  So, if you find that the battery is heating abnormally during use or charging,  you must not ignore it anymore.

There are two main types of battery heating:

1、 Heating during  battery discharge refers to abnormal heating of the battery during  use;

2、 It is the battery  that heats up during charging. The reasons for abnormal heating of batteries  vary under different circumstances.

1. Reason for battery discharge heating: Discharge too fast,  possibly due to low battery capacity and discharge current exceeding 0.5C for a  long time. It is emphasized that after a short distance driving, although the  battery consumes a certain amount of electricity, it undergoes a recovery  process after being stationary, and the electrochemical process of the electrode  plate continues. Therefore, the voltage will rise slightly, but it does not mean  that the capacity will rise; On the contrary, during long-distance driving  without stopping, the electrification of the electrode plate and the consumption  of electrical energy occur simultaneously, which can lead to three  situations:

① When the rated voltage of the motor is low,  the battery capacity is small, and the working current is too high, the voltage  will sharply decrease, and the capacity will be quickly consumed, which is the  most unfavorable for the battery.

② The electrochemical reaction speed of the  battery can only maintain driving, and there is no chance for the battery to  recover or gasp. It often undergoes full cycle charging and discharging, which  can lead to excessive consumption if not paid attention. When encountering  uphill winds, the power consumption is very high, forcing the battery plates to  react rapidly. The high heat of the battery shell can damage the battery,  shorten its lifespan, and indicate that the capacity is not  abundant.

③ Ideally, the electrochemical reaction rate  of the battery can provide sufficient electrical energy calmly. The shell of the  battery has no abnormal heat, indicating that the battery capacity is  surplus.

Only the last of the three situations is ideal for long-distance  driving. It should be noted that the outer shell of the battery is noticeably  hot, and the heat of the internal battery itself is even  higher.

2. The reason for the heating during battery charging: During the  charging process, a portion of the electrical energy is converted into chemical  energy, while another portion is converted into thermal and other energy.  Heating of rechargeable batteries is a normal phenomenon, but when the  temperature is high, it is necessary to promptly check whether the charging  current is too high or if there is a short circuit inside the  battery.

The relationship between heat generation and electrolyte quantity  is relatively small. For example, when the electrolyte quantity of sealed  batteries is low, the internal resistance increases, which can also cause the  battery to heat up and the terminal voltage during charging is very high. Aging  of batteries, drying of electrolyte, and internal short circuits can also cause  heating. The charger cannot maintain a constant voltage during the later stage  of charging, which can cause the battery voltage to exceed the allowable value,  resulting in an increase in temperature and, in severe cases, swelling, and the  end of its lifespan.

During use, try not to lay it horizontally or upside down to  prevent a large amount of gas generated inside the battery from being discharged  smoothly from the vent valve, especially during charging, otherwise it may cause  the shell to burst.

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