Overcharging of lead-acid batteries refers to the phenomenon where the battery continues to receive charging current after being fully charged, resulting in excessive chemical reactions inside the battery. Overcharging can seriously damage battery life and pose safety risks (such as swelling, leakage, and fire). The following are specific scenarios and judgment criteria, combined with energy storage/portable power usage scenarios (such as solar charging and backup power commonly used in the African market) for detailed explanation:
1、 Core judgment criteria (essence of overcharging)
After a lead-acid battery is fully charged, the voltage will reach its peak (usually the full charge voltage of a 12V single battery is 13.8~14.4V, and 24V is 27.6~28.8V). At this time, if the charging voltage exceeds the upper limit of the rated float charging voltage, or the charging current continues to be greater than the battery's self discharge current (generally ≤ 0.05C, where C is the battery capacity), and the duration exceeds 1-2 hours, it is considered overcharging.
2、 Common overcharging scenarios (combined with energy storage/portable power usage scenarios)
1. Mismatch of charging device parameters (most common)
Charging voltage too high: The output voltage of the charger/solar controller used exceeds the upper limit of the battery's rated voltage (for example, a 15V charger is used for a 12V battery, and a 30V solar panel is used for direct charging of a 24V battery), causing the battery to be forcibly injected with current even after being fully charged.
Excessive charging current: The rated current of the charger far exceeds the allowed charging current of the battery (for example, using a 50A fast charging charger for a 100Ah battery, far exceeding the safe charging rate of 0.3C~0.5C). Even if the voltage does not exceed, continuous charging with high current will cause internal heating and gas evolution of the battery, which is equivalent to overcharging.
Charging mode error: Using "constant current charging" mode instead of "three-stage charging" (constant current → constant voltage → float charging), the battery is not switched to float charging mode after being fully charged, and continues to charge with a fixed current (commonly seen in cheap solar controllers and simple chargers).
2. Charging time is too long (due to human or equipment malfunction)
Forgetting to cut off power artificially: After the battery is fully charged (such as 8-10 hours after solar charging), it is not disconnected in time and continues to charge for more than 12 hours (for example, in rural Africa, forgetting to turn off solar charging at night, resulting in the battery being overcharged all night).
Equipment failure unable to power off: The fully charged power-off function of the charger and controller fails (such as damaged voltage sensors or stuck relays), and even if the battery is fully charged, the device continues to output current.
3. Poor consistency of battery pack (multi string battery scenario)
When multiple batteries are used in series (such as a 48V energy storage power supply composed of four 12V batteries), if one battery has a low capacity and high internal resistance, it will be fully charged first during charging, but the other batteries will not be fully charged. The charger will continue to supply power, causing the first fully charged battery to be overcharged ("short board effect").
4. Hidden overcharging caused by special usage environments
High temperature environment charging: Outdoor temperatures in Africa often reach 35-45 ℃ during the day. High temperatures can reduce the battery's charging capacity, causing the battery to reach a "false full charge" state ahead of time. If the charger does not have temperature compensation function and still charges at room temperature voltage, it will cause actual overcharging (for example, the floating charge voltage of a 12V battery is 13.8V at normal temperature, and it should be reduced to 13.2-13.5V at high temperature, otherwise overcharging).
Low temperature environment charging: Low temperature (such as 0-10 ℃ at night on the African plateau) will increase the internal resistance of the battery, causing the voltage to rise too quickly during charging. The charger may mistake it as "fully charged" and stop charging, but the actual battery is not fully charged; If the temperature rises and the battery voltage drops in the future, and the charger starts charging again, it may lead to multiple "supplements" causing overcharging.
5. Overcharge sensitivity caused by battery aging or damage
Aging batteries (used for more than 2 years) have active material detachment on the electrode plates, electrolyte loss, rapid voltage rise during charging, and severe gas evolution. Even if the charging parameters are normal, it is easy to experience a situation of "seemingly fully charged but actually overcharged" (manifested as battery heating and bulging).
3、 Typical manifestations of overcharging (easy to quickly identify)
The battery casing heats up severely (when charging, the temperature exceeds 40 ℃, and even burns your hands);
There is a pungent odor at both ends of the battery/safety valve (a mixture of hydrogen and oxygen gas produced by gas evolution, or a sour taste from electrolyte leakage);
The battery shell bulges and deforms (internal gas cannot be discharged in a timely manner, causing the shell to expand);
The electrolyte level drops too quickly (overcharging causes electrolyte decomposition and evaporation, and opening the injection hole reveals that the liquid level is lower than the electrode plate);
The current does not decrease continuously during charging (the current should drop to 0.01~0.05C after normal full charge, and if it still remains above 0.1C, it may be overcharging).
4、 Recommendations for preventing overcharging in energy storage/portable power scenarios (for the African market)
Choose a charger/solar controller with three-stage charging and temperature compensation (prioritize controllers that support PWM/MPPT and are suitable for complex lighting conditions in Africa);
Strictly match charging parameters: charger voltage=battery rated voltage × 1.1~1.15 (e.g. 13.8~14.4V charger for 12V battery), charging current ≤ 0.5C (e.g. ≤ 50A charger for 100Ah battery);
Avoid long-term unattended charging: pair with a timer switch (such as the mechanical timer socket commonly used in Africa), set the charging time (8-10 hours), or choose a smart device with full charge power-off function;
Regularly check the consistency of the battery pack: When using multiple series of batteries, check the voltage of a single battery every 3-6 months. If there is inconsistency, charge it evenly or replace the short battery in a timely manner;
Optimize charging in high temperature environments: Avoid direct sunlight during noon (11:00~15:00) for charging, or install heat dissipation devices (such as ventilation enclosures) on the battery, and choose equipment that supports high temperature voltage compensation.
By identifying and implementing preventive measures in the above scenarios, it is possible to effectively prevent overcharging of lead-acid batteries and extend their service life in energy storage/portable power scenarios (especially suitable for high-temperature and unstable lighting environments in Africa).
