- The voltage of the battery
The nominal voltage of each cell of the battery is 2V, and the actual voltage varies with charging and discharging. At the end of charging, the voltage is 2.5~2.7V, and then it slowly drops to a steady state of about 2.05V.
If the battery is used as the power source, the voltage will drop to about 2V quickly when the discharge starts, and then slowly drop to keep it between 1.9V and 2.0V. When the discharge is close to the end, the voltage quickly drops to 1.7V; when the voltage is lower than 1.7V, it will no longer discharge, otherwise the electrode will be damaged. After stopping use, the battery voltage can rise to 1.98V by itself.
- The capacity of the battery
(1) The concept of battery capacity. The amount of electricity that a lead-acid battery in a fully charged state can give when discharged to a specified end voltage under certain discharge conditions is called the battery capacity, which is represented by the symbol C. The commonly used unit is ampere hour, abbreviated as ampere hour (A·h). The discharge time rate is usually indicated at the lower corner of C. For example, C10 indicates the discharge capacity of 10 hours, and C120 indicates the discharge capacity of 120 hours. The battery capacity is divided into theoretical capacity, actual capacity and rated capacity. The theoretical capacity is the highest capacity value calculated according to Faraday’s law based on the mass of the active material. The actual capacity refers to the amount of electricity the battery can output under certain discharge conditions. When forming a battery, in addition to the main reaction of the battery, there are side reactions that occur. In addition to various other reasons, the utilization rate of the active material cannot be 100%, so it is far lower than the theoretical capacity. The rated capacity is also called the nominal capacity abroad. It is in accordance with the standards promulgated by the country or relevant departments. The battery is required to be discharged under certain discharge conditions during battery design (communication batteries generally stipulate that the current is discharged to the termination voltage at a rate of 10 hours under a 25°C environment. ) The minimum amount of electricity that should be discharged.
(2) Factors affecting the actual capacity of the battery. The actual capacity of the battery is mainly related to the quantity and utilization of the positive and negative active materials of the battery. The utilization rate of active materials is mainly affected by the discharge system, electrode structure, and manufacturing process. What affects the actual capacity during use is the discharge rate, discharge system, termination voltage and temperature.
- The discharge rate of the battery
According to the size of battery discharge current, it is divided into time rate and current rate. The time rate refers to the length of time from discharge to the end of discharge voltage under certain discharge conditions. Commonly used time rate and magnification. According to the 1EC standard, the discharge time rate has 20, 10, 5, 3, 1, 0.5 hour rates, which are respectively identified as 20h, 10h, 5h, 3h, 1h, 0.5h, etc. The higher the battery discharge rate, the greater the discharge current, the shorter the discharge time, and the less the corresponding capacity released.
- The end voltage of the battery
The termination voltage refers to the lowest operating voltage at which the battery discharge voltage drops to the point where it is no longer suitable for discharging (at least it can be recharged and used repeatedly). In order to prevent damage to the plates, various standards stipulate the termination voltage of the battery when discharging at different discharge rates and temperatures. The termination voltage of the 10-hour rate and 3-hour rate discharge of the backup power series battery is 1.80V/cell, and the 1-hour rate termination voltage is 1.75V/cell. Due to the characteristics of lead-acid batteries, even if the discharge termination voltage continues to decrease, the battery will not release too much capacity, but the termination voltage is too low to cause great damage to the battery, especially when the discharge reaches 0V and cannot be charged in time. Greatly shorten the life of the battery. For solar batteries, the end-of-discharge voltage design is different for different models and uses. The final voltage depends on the discharge rate and requirements. Generally, for a small current discharge less than 10h, the termination voltage is slightly higher; for a large current discharge greater than 10h, the termination voltage is slightly lower.
- Cycle life of battery
The battery undergoes a charge and discharge, which is called a cycle (a cycle). Under certain discharge conditions, the number of cycles the battery can withstand before the battery is used to a certain capacity is called the cycle life. The backup power supply generally uses the floating charge life to measure the battery life. For example, the floating charge life of a valve-regulated sealed lead-acid battery is generally more than 10 years, but the cycle life of the battery can also be used to measure. The main factor that affects the cycle life of the battery is the performance and quality of the product, followed by the quality of the maintenance work. For the back-up power supply, 100% DOD discharge, the cycle life is generally 100~200 times, that is, the battery discharges 100% capacity, the battery discharges to the end voltage of 1.8V/pc, after 100~200 cycles, the battery discharges to the end voltage 1.8V, the discharge capacity is lower than 80% of the rated capacity, and the battery life ends at this time. The factors that affect the battery life are comprehensive factors, not only the internal factors of the plate, such as the composition of the active material, crystal type (high temperature curing or normal temperature curing), plate size and grid material structure, etc., but also depend on external factors , Such as discharge rate and depth, working conditions (temperature and pressure, etc.) and maintenance conditions, etc.
- The internal resistance of the battery
The internal resistance of the battery is not constant, and it changes continuously over time during the charge and discharge process, because the composition of the active material, the electrolyte concentration and the temperature are constantly changing. The internal resistance of lead-acid batteries is very small and can be ignored when discharging with a small current, but when discharging with a large current, the voltage drop loss can reach hundreds of millivolts, which must be paid attention to.
The internal resistance of the battery has two parts: ohmic internal resistance and polarization internal resistance. The ohmic resistance is mainly composed of electrode material, diaphragm, electrolyte, terminal, etc. It is also related to battery size, structure and assembly factors. Polarized internal resistance is caused by electrochemical polarization and concentration polarization, and is the internal resistance generated by polarization when the two electrodes undergo a chemical reaction during battery discharge or charging. Polarization resistance is not only related to battery manufacturing process, electrode structure and activity of active materials, but also related to factors such as battery operating current and temperature. The internal resistance of the battery seriously affects the battery’s operating voltage, operating current and output energy, so the smaller the internal resistance, the better the battery performance.