Teach you how to use a multimeter to judge the quality of the rechargeable battery
1. Rechargeable battery
(1) Charging rate (C-rate)
C is the first letter of Capacity, which is used to indicate the magnitude of the current when the battery is charged and discharged.
For example, when the rated capacity of the rechargeable battery is 1100mAh, it means that the discharge time at 1100mAh (1C) can last for 1 hour. If the discharge time at 200mA (0.2C) can last for 5 hours, the charging can also be calculated according to this comparison.
(2) Cut-offdischarge voltage
Refers to when the battery is discharged, the voltage drops to the minimum working voltage value that the battery should not continue to discharge.
According to different battery types and different discharge conditions, the requirements for the capacity and life of the battery are also different, so the specified termination voltage of battery discharge is also different.
(3) Open circuit voltage (OpencircuitvoltageOCV)
When the battery is not discharging, the potential difference between the two poles of the battery is called the open circuit voltage.
The open circuit voltage of the battery will vary according to the material of the positive and negative electrodes of the battery and the electrolyte. If the materials of the positive and negative electrodes of the battery are exactly the same, no matter how big the battery is and how the geometry changes, the open circuit voltage will be the same.
(4) Depth of discharge DOD
During the use of the battery, the capacity released by the battery as a percentage of its rated capacity is called the depth of discharge.
The depth of discharge has a deep relationship with the charging life of the secondary battery. The deeper the depth of discharge of the secondary battery, the shorter the charging life. Therefore, deep discharge should be avoided as much as possible in use.
(5) Overdischarge (Overdischarge)
If the battery exceeds the termination voltage value of battery discharge during the discharge process, and continues to discharge, the internal pressure of the battery may increase, the reversibility of the positive and negative active materials will be damaged, and the capacity of the battery will be significantly reduced.
(6) Overcharge
When the battery is charging, if it continues to be charged after it is fully charged, it may cause the internal pressure of the battery to rise, the battery to deform, and to leak at night, and the performance of the battery will also be significantly reduced and damaged.
(7) Energy density (Energydensity)
The electrical energy released by the average unit volume or mass of a battery.
Generally, under the same volume, the energy density of lithium-ion batteries is 2.5 times that of nickel-cadmium batteries and 1.8 times that of nickel-metal hydride batteries. Smaller size and lighter weight.
(8) Self-discharge (Selfdischarge)
Regardless of whether the battery is in use or not, due to various reasons, it will cause the phenomenon of power loss.
If calculated in units of one month, the self-discharge of lithium-ion batteries is about 1%-2%, and the self-discharge of nickel-metal hydride batteries is about 3%-5%.
(9) Charging cycle life (Cyclelife)
When the rechargeable battery is repeatedly charged and discharged, the battery capacity will gradually decrease to 60%-80% of the initial capacity.
(10) Memory effect (Memoryeffect)
During the charging and discharging process of the battery, many small bubbles will be generated on the battery plate. Over time, these bubbles will reduce the area of the battery plate and indirectly affect the capacity of the battery.
2. How to use a multimeter to judge the quality of the rechargeable battery
The following is an example of a lithium-ion battery with a standard voltage of 4.2V.
If the voltage after full charge is 4.2V, it means it's OK. If the battery is used for more than 0.7 times the time of the new battery, it means the battery is not bad. If the voltage after full charge is higher than 4.2V, it means there is something wrong with the charger. Voltmeter must be accurate). Please see the introduction below.
(1) The nominal voltage of the lithium-ion battery is 3.7V (3.6V), and the charging cut-off voltage is 4.2V (4.1V, which has different designs according to the brand of the battery). (The specification for lithium-ion batteries is: lithium-ion secondary batteries)
(2) Charging requirements for lithium-ion batteries (GB/T182872000 specification): First, constant current charging, that is, the current is constant, and the battery voltage gradually increases with the charging process. When the battery terminal voltage reaches 4.2V (4.1V), change to constant current. Current charging is constant voltage charging, that is, the voltage is constant, and the current gradually decreases as the charging process continues according to the saturation degree of the cell. When it decreases to 0.01C, the charging is considered to be terminated. (C is a way of expressing the nominal capacity of the battery against the current. For example, if the battery has a capacity of 1000mAh, 1C is the charging current of 1000mA. Note that it is mA instead of mAh, and 0.01C is 10mA.) Of course, the standard representation is 0.01 C5A, I simplified it here.
(3) Why do you think that 0.01C is the end of charging: this is stipulated by the national standard GB/T18287-2000, and it is also discussed. In the past, everyone generally ended with 20mA. The industry standard YD/T998-1999 of the Ministry of Posts and Telecommunications also stipulates that no matter how large the battery capacity is, the stop current is 20mA. The 0.01C specified by the national standard helps to charge more fully, which is beneficial for the manufacturer to pass the appraisal. In addition, the national standard stipulates that the charging time should not exceed 8 hours, that is to say, even if it has not reached 0.01C, it is considered that the charging is over after 8 hours. (Batteries with good quality should reach 0.01C within 8 hours, batteries with poor quality, it is meaningless to wait)
(4) Since there is a protection board in the battery, can we rest assured: No, because the cut-off parameter of the protection board is 4.35V (this is still good, the worse is 4.4 to 4.5V), the protection board is to deal with the emergency Yes, if it is overcharged every time, the battery will decay quickly.
(5) How much charging current is appropriate: in theory, the smaller the better the battery. But you can't wait 3 days for a battery to charge. The low rate charging specified by the national standard is 0.2C (arbitration charging system). Taking the above 1000mAh battery as an example, it is 200mA. Then we can estimate that this battery can be fully charged in more than 5 hours. (Capacity mAh = current mA × time h) The national technical supervision department identifies the lithium battery capacity, which is charged at a high rate of 1C, discharged at a low rate of 0.2C, and the capacity value is calculated by time. The number of tests is 5, and there is 1 capacity. reach the end of the test. (That is, there are 5 chances. If the first test is qualified, the next 4 times will not be done.) Before the test, a pre-cycle is allowed, that is, charging with 1C constant current to 4.2V will stop, and there will be no subsequent constant voltage to 0.01C process, not even 14 hours.
(6) How much charging current can the lithium-ion battery withstand: It can be very high during the manufacturer's test, but the national standard high rate is 1C. Taking the above battery as an example, it can be fully charged in more than 1 hour. Can the battery withstand such a large charging current? For the current lithium-ion batteries, it is just trivial. At present, there is no national standard for chargers, but the industry standard YD/T9981999/2 of the Ministry of Posts and Telecommunications is implemented, which stipulates that the current of the charger shall not be greater than 1C.
(7) How the life is defined: Simply put, it means that the capacity of the battery drops to 70% after N times of 1C charge and 1C discharge, and the N at this time is the life. It doesn't mean that 300 times can still be used, and 301 times can't be used. The national standard stipulates that the lifespan shall not be less than 300 times. The conditions we usually use are not as harsh as the test, and the lifespan will be longer.
