# How to Correctly Connect Lithium Batteries in Series And in Parallel?

The purpose of parallel connection of lithium batteries is to increase the capacity. Therefore, parallel charging of lithium batteries has different design characteristics compared with single-cell lithium batteries, mainly reflected in the consistency of charging current design and parallel battery.

The characteristics of the parallel lithium battery are: the voltage is constant, the battery capacity is added, the internal resistance is reduced, and the power supply time is prolonged. The core content of parallel charging is the size of the parallel current and its effect. According to the parallel theory, the main circuit current is equal to the sum of the currents of the respective branches. Therefore, the multi-section parallel lithium battery that has been combined into a battery pack should achieve the same charging efficiency as the single-cell battery, and the charging current should be the sum of the currents of the plurality of lithium batteries. Under the formula of Ohm's law: I=U/R, this design is reasonable. However, the internal resistance of the battery in parallel will also change. According to the parallel internal resistance formula, the total internal resistance of the two parallel lithium batteries is equal to the ratio of the sum of the internal resistance products of the two batteries and the internal resistance. The parallel resistance will follow. The number of parallel batteries increases and decreases. Therefore, the efficiency of parallel charging of lithium batteries can be achieved on the basis of the current less than the sum of the currents of n parallel lithium batteries. Lithium battery parallel should pay attention to the consistency of the battery, because the parallel lithium battery with poor consistency will not charge or overcharge during the charging process, thus destroying the battery structure and affecting the life of the whole battery. Therefore, when using parallel batteries, avoid mixing lithium batteries of different brands, different capacities and different old and new levels. The inherent requirements for battery consistency are: lithium battery cell voltage difference ≤ 10mV, internal resistance difference ≤ 5mΩ, capacity difference ≤ 20mA.

In fact, after the lithium battery is connected in parallel, there will be a charging protection chip to protect the lithium battery. The lithium battery manufacturer has fully considered the variation characteristics of the lithium battery in parallel when making the parallel lithium battery, and also designed the current according to the above requirements. The battery is selected, so the user needs to follow the instructions of the parallel lithium battery to charge step by step to avoid damage to the battery caused by incorrect charging.

The battery series voltage is equal to the sum of the battery voltages of the string, the voltage is increased, the bulbs are connected in series, and one switch can control all the bulbs connected in series on one line.
The use of the pool in series can increase the output voltage. What are the characteristics of the bulbs in series: the sum of the voltages of the two bulbs is the total voltage of the circuit.

After the batteries are connected in series, the voltages are added, and the currents are equal, which increases the voltage; the batteries are connected in parallel, and the voltage is constant (provided that the batteries with voltages can be connected in parallel, otherwise the high voltage will charge the voltage low, if the difference is too large, There is also a danger) that the current is equal to the sum of the individual batteries, which is often considered to increase the battery capacity and provide more current.

The voltage increases and the capacity does not change.

The difference between battery series and parallel:
Battery in series:
It means that the battery is connected end to end. That is, the positive pole of the first battery is connected to the negative pole of the second battery, and the positive pole of the second battery is connected to the negative pole of the third battery, and so on;
The series voltage is equal to the sum of the battery voltages, and the current is equal to the current flowing through each battery;
A damage in one of the battery packs will cause the entire battery pack to be unusable or the voltage to drop;
Series connection can increase the total voltage.
Battery in parallel:
It means that the first head of the battery is connected and the tail is connected. That is, the positive poles of all the batteries are connected, and the negative poles of all the batteries are connected.
The shunt voltage is equal to the individual battery voltage and the current is equal to the sum of the battery currents.

Although the battery life of the battery pack is enhanced, the damage caused by the short-circuit current is more serious;
Parallel can increase the total current.
1. When the batteries are connected in parallel, the voltages are equal everywhere, that is, Ua=Ub=Uc=Uo; the current is the sum of the currents of the respective batteries, that is, Io=Ia+Ib+Ic. (See Figure 1 for a parallel circuit of the battery)
The battery is connected in parallel for the case where the voltage is constant and the current needs to be increased.
2. When the batteries are connected in series, the currents are equal everywhere, that is, Io=Ia=Ib=Ic; the voltage is the sum of the voltages of the respective batteries, that is, Uo=Ua+Ub+Uc. (See Figure 2 for the series circuit of the battery)

The battery is used in series for applications where the current is constant and the voltage needs to be increased.

Whether in series or in parallel, the output power of the battery pack increases.

Parallel: Several batteries, positive and negative, negative and negative are connected side by side, the voltage is constant, the capacity increases, and the corresponding current also increases. Tandem: Several battery head-to-tail strings are positive and negative together, the first section is negatively connected to the second section, and so on. The voltage increases and the capacity does not change. That is to say, if they are connected in series, the electromotive force is the sum of the electromotive forces of the two batteries. If they are connected in parallel, the voltage they provide to the electrical appliances is as large as the electromotive force of only one battery. I hope my answer can help you! I am also learning this part of the knowledge, it is difficult,
When connected in series, the voltage is the sum of the two battery voltages. When connected in parallel, the voltage is equal to the voltage of the two batteries
Increase the voltage in series and increase the capacity in parallel. For example, if you have two 1.5 volt, 2000 mAh batteries, you will get a 3 volt, 2000 mAh battery in series, and a 1.5 volt, 4000 mAh battery in parallel.
1. When the batteries are connected in parallel, the voltages are equal everywhere, that is, Ua=Ub=Uc=Uo; the current is the sum of the currents of the respective batteries, that is, Io=Ia+Ib+Ic. (See Figure 1 for a parallel circuit of the battery)
The battery is connected in parallel for the case where the voltage is constant and the current needs to be increased.
2. When the batteries are connected in series, the currents are equal everywhere, that is, Io=Ia=Ib=Ic; the voltage is the sum of the voltages of the respective batteries, that is, Uo=Ua+Ub+Uc. (See Figure 2 for the series circuit of the battery)

The battery is used in series for applications where the current is constant and the voltage needs to be increased.

Whether in series or in parallel, the output power of the battery pack increases. 1. in series, the current is constant, the voltage is added; in parallel, the voltage is constant, the current is added
2. although the voltage has not changed, the two 12v batteries are connected in series in order to obtain higher voltage to adapt to the electrical appliances. It is necessary to have a current of 10A above 100w, such as an inverter with a design value of 12v input, which is for switches and wires. The requirements are extremely high, so reducing the current is the main reason, it is necessary to connect two parallels, but the normal discharge current is allowed to double, if the current is only 5A when using 24v. Therefore, many places use high-voltage electrical appliances (such as electric vehicles). But some appliances are originally 12v. When their power (current) is large, the electric motor, in order to increase the working time of the battery or the current of a single battery is not enough to drive, the battery is only 12v, and the power of some electric appliances is relatively large.
The two 6V batteries are connected in series at 12V. The two 12V batteries are only 12V in parallel. The so-called parallel connection is the positive pole connected to the positive pole and the negative pole connected to the negative pole.

The two 12v batteries are connected in series in order to obtain higher voltage to adapt to the electrical appliances. The battery is only 12v, and some of the electrical appliances have relatively large power. The current of 10A is more than 100w, which is extremely demanding for switches and wires. If the current is only 5A when using 24v, the current is the main reason, so many places use high-voltage electrical appliances (such as electric vehicles). This is also the case. However, some appliances are originally 12v, for example, the design value is 12v input. Inverter, motor... When their power (current) is large, in order to increase the working time of the battery or the current of a single battery is not enough to drive, two parallel connections are required, although the voltage does not change, but the normal discharge is allowed. The current has doubled.

The difference between battery parallel and series is mainly the difference in voltage and capacity. Take the voltage of 3.7V, the capacity is 3000mAh lithium battery, the same is two batteries, if it is two strings, then the battery model is: 7.4V /3000mAh, if it is two, the model will become: 3.7V/6000mAh. When connected in series, the voltage increases and the capacity does not change. When connected in parallel, the capacity is increased and the voltage is constant. But the batteries we often use are all connected in series and parallel, for example: three strings and four. I hope I can help you.

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