Teach you how to use a multimeter to judge the quality of rechargeable batteries

1. Rechargeable battery
1. Charging rate (C-rate)
C is the 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 of 1100mAh (1C) can last for 1 hour. If the discharge time of 200mA (0.2C) can last for 5 hours, the charging can also be calculated according to this comparison.

2. Cut-offdischargevoltage

When the battery is discharged, the voltage drops to the operating voltage value at which the battery is no longer suitable for discharging.

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 terminal voltage of the battery discharge is also different.

Teach you how to use a multimeter to judge the quality of rechargeable batteries

3. Open circuit voltage (OpencircuitvoltageOCV)
When the battery is not discharged, the potential difference between the two poles of the battery is called the open circuit voltage.

The open circuit voltage of the battery varies according to the materials of the battery's positive, negative and electrolyte. If the materials of the battery's positive and negative electrodes are exactly the same, then the open circuit voltage will be the same regardless of the size of the battery and how the geometric structure changes.

4. Depth of discharge (DepthofdischargeDOD)
In the process of battery use, the percentage of the battery's rated capacity is called the depth of discharge.

The depth of discharge has a deep relationship with the charging life of the secondary battery. When the depth of discharge of the secondary battery is deeper, the charging life will be shorter. Therefore, deep discharge should be avoided as much as possible during use.

5. Overdischarge
If the battery exceeds the battery discharge termination voltage during the discharge process, the internal pressure of the battery may increase when the battery continues to be discharged, the reversibility of the positive and negative active materials will be damaged, and the battery capacity will be significantly reduced.

6. Overcharge
When the battery is charging, if it continues to charge after it reaches a fully charged state, it may cause the internal pressure of the battery to increase, battery deformation, night leakage, etc., and the performance of the battery will also be significantly reduced and damaged.

Teach you how to use a multimeter to judge the quality of rechargeable batteries

7. Energy density (Energydensity)
The electric energy released by the average unit volume or mass of a battery.

Generally, in 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-hydrogen batteries. Therefore, when the battery capacity is equal, lithium-ion batteries will be better than nickel-cadmium and nickel-hydrogen batteries. Smaller size and lighter weight.

8. Selfdischarge
Regardless of whether the battery is used or not, due to various reasons, it will cause the phenomenon of power loss.

If calculated in a month, the self-discharge of lithium-ion batteries is about 1%-2%, and the self-discharge of nickel-hydrogen batteries is about 3%-5%.

9. Charging cycle life (Cyclelife)
When the rechargeable battery is repeatedly charged and discharged, the battery capacity gradually decreases 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 battery capacity.

Second, how to use a multimeter to judge the quality of rechargeable batteries
The following takes a lithium-ion battery with a standard voltage of 4.2V as an example.

If the battery voltage is 4.2V after being fully charged, it is okay. If the battery is used for more than 0.7 times the time of a new battery, then the battery is not bad. If the battery voltage is higher than 4.2V after being fully charged, it indicates that the charger has a problem. (Note The voltmeter must be accurate). Please see the introduction below.

1. The nominal voltage of lithium-ion battery is 3.7V (3.6V), and the charging cut-off voltage is 4.2V (4.1V, according to the battery brand, there are different designs). (The specification of lithium ion batteries is: lithium ion secondary batteries)

2. Requirements for lithium-ion battery charging (GB/T182872000 specification): First, constant current charging, that is, a certain current, and the battery voltage gradually increases with the charging process, when the battery terminal voltage reaches 4.2V (4.1V), change to constant 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 of the battery. 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. 0.01C is 10mA.) Of course, the standard expression is 0.01 C5A, I simplified it here.

Teach you how to use a multimeter to judge the quality of rechargeable batteries

3. Why 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 up 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 stipulated by the national standard helps to charge more fully, which is beneficial for the manufacturer to pass the identification. In addition, the national standard stipulates that the charging time should not exceed 8 hours, that is, even if it has not reached 0.01C, the charging is considered to be 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 bad one should be 4.4 to 4.5V), the protection board is to deal with it in case If the battery is overcharged every time, the battery will decay quickly.

5. What charging current is appropriate: In theory, the smaller the battery, the more beneficial it is. But you can't wait 3 days to charge a battery. 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&TImes; time h) The national technical supervision department appraised the capacity of lithium battery. It is charged at a high rate of 1C and discharged at a low rate of 0.2C. 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 test is qualified, the next 4 times are not done) Pre-cycle is allowed before the test, which is to charge with 1C constant current to 4.2V and stop, and there is no subsequent constant voltage to 0.01C The process, not to mention 14 hours.

Teach you how to use a multimeter to judge the quality of rechargeable batteries

6. How much charging current the lithium-ion battery can withstand: It can be very high during the manufacturer's test, but the high rate of the national standard is 1C, and the battery above 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's just a trivial matter. There is currently no national standard for chargers. 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. What is the life expectancy: In short, it means that after N times of 1C charge and 1C discharge, the capacity of the battery drops to 70%. At this time, N is the lifespan. It's not that you can use it 300 times, but you can't use it 301 times. The national standard stipulates that the life span shall not be less than 300 times. The conditions we usually use are not as harsh as the testing, and the lifespan will be longer.