As a core component of the UPS power supply system, the battery plays a key role in storing electric energy, coping with the abnormal and special working conditions of the power grid, and maintaining the normal operation of the system. It is the last line of defense for the normal operation of the power system.

At present, the battery online monitoring is gradually being paid attention to, in the electric power, communication and other industries more and more widely used, but the battery online monitoring and status assessment of the key technology - internal resistance AC discharge method is not understood by people, but also in the vague understanding, due to the "maintenance-free" the word misleading, so that users relax the battery daily maintenance and management, The early capacity of the battery is reduced and damaged. Therefore, the correct use and maintenance of battery, improve its service life, has very important significance.

The main factors that affect the internal resistance of the battery are:

With the increase of the use of time, the electrolyte water loss, plate and connection strip corrosion, plate acidification, plate deformation and active material shedding and other factors, resulting in the reduction of battery capacity, battery internal resistance increases.

Due to the depth of the electrolyte injected into the battery, the thickness of the reaction material on the electrode surface, the porosity of the electrode surface and so on, the internal resistance of the battery is relatively large, so the amount of charge is also relatively large.

When the ambient temperature changes, such as rising, the diffusion of the reactive substance is accelerated, the charge transfer, the electrode dynamics process and the material transfer are easier to carry out, and thus the internal resistance of the battery is reduced. If not, it will increase.

Different production plants, different kinds, different models of batteries, due to the electrode, electrolyte, diaphragm material formula is different, the battery structure is different, assembly process is different and the battery internal resistance is different.

At present, many battery internal resistance measurements actually measure the impedance of the battery, which includes the capacitive reactance of the battery, and the size of the capacitive reactance is related to the measurement signal frequency, so the battery internal resistance measurement results are not objective. To be objective, the effect of battery capacitance on the measurement results should be removed analytically according to the phase relationship between the current and voltage of the measurement signal, so that the measurement rate results are independent of the signal measurement frequency, that is, the internal resistance measurement results are unique under any measurement signal frequency.

In the case of large measurement current, at the moment when the measurement signal is applied and the measurement signal is turned off, because the establishment and stability of polarization is a changing process, different measurement current, different measurement time, the polarization is different, so that the battery internal resistance measurement results are not objective. To be objective, the internal resistance should be measured with a small signal current as far as possible. According to the experiment, the measured current is less than or equal to 0.05C10 (where C10 is the capacity of the battery at a 10-hour discharge rate).

In the long-term overcharging state, water is consumed in the positive electrode due to oxygen evolution reaction, and h+ increases, which leads to increased acidity near the positive electrode and accelerated grid corrosion, thus thinning the grid and accelerating the corrosion of the battery and reducing the battery capacity. At the same time, due to the increased water loss, will make the battery dry risk, thus affecting the battery life.

Battery overcharge occurs when the AC power fails, and the battery supplies power for a long time. When the voltage of the battery is too low or even zero, a large amount of lead sulfate in the battery will be absorbed to the cathode surface of the battery, resulting in "sulphate" at the cathode of the battery. Lead sulfate is a kind of insulator, and its formation will have a great negative impact on the charging and discharging performance of the battery. Therefore, the more sulfate formed on the cathode, the greater the internal resistance of the battery, the worse the charging and discharging performance of the battery, and the shorter the service life of the battery.