Most electric vehicles today use sealed lead-acid batteries. Lead-acid batteries do not require frequent water replenishment, are maintenance-free, have low cost, high cost-effectiveness, and can be reused. However, lead-acid batteries have many problems during use. To extend the lifespan of electric vehicle batteries, it is necessary to have a basic understanding of these problems. Adopting correct usage methods will better ensure the battery's lifespan.
Why should batteries be recharged before first use? Batteries typically take 1-2 months, or even longer, to go from manufacturing to use. During storage, due to self-discharge and other spontaneous reactions within the battery, some of its power is consumed, and it may not reach its rated capacity. Therefore, it is best to recharge the battery before first use to avoid customers mistakenly believing that the capacity is insufficient.
If an electric vehicle is to be stored for an extended period of time, the battery should be properly handled as follows: First, the battery should be fully charged before storage, and it should be charged at least once a month to prevent it from being depleted. This can effectively prevent the formation of dendrites that can cause irreversible salification and dendrite short circuits.
Should the battery be fully discharged before charging? Unlike other secondary batteries, lead-acid batteries have no memory effect. Therefore, regardless of the battery's state of charge, they can be charged directly without discharging.
Is it better to charge a battery frequently or fully discharge it before recharging? Since shallower discharges significantly increase the number of battery cycles, theoretically, frequent charging is beneficial for cycle life. However, many chargers on the market suffer from high failure rates, poor reliability, and low accuracy due to price and technological limitations. Therefore, frequent charging can sometimes actually shorten battery life. While fully discharging the battery before recharging reduces the number of charging cycles, the inherent differences between individual cells during discharge can cause some cells to over-discharge. Over-discharged batteries have significantly reduced charging capacity, leading to undercharging. Furthermore, fully discharging before recharging puts the charger under heavy load for an extended period, potentially damaging it. Therefore, considering all factors, we believe that charging the battery when it has discharged 50-70% of its capacity is more reasonable and beneficial for battery life.
What are the harms of overcharging and undercharging? Overcharging occurs when the battery charging current exceeds the battery's acceptable current; the excess is the overcharge. The main problem with overcharging is the side reaction of water electrolysis. Because oxygen transfers from the positive electrode to the negative electrode and undergoes oxygen recombination, heat is generated. Therefore, the overcharge effectively converts into heat, raising the battery temperature. If left uncontrolled, this can lead to significant water loss, and in severe cases, thermal runaway, drastic capacity reduction, and even deformation. Undercharging, simply put, means the battery is frequently undercharged. This causes the gradual formation of coarse, hard lead sulfate at the electrodes, which is almost insoluble, a condition known as irreversible sulfation. Ordinary charging methods cannot be used to replenish this sulfate, resulting in rapid capacity decay with each charge.
