Definition of Series and Parallel Connections for Lithium Battery Cells

Due to the limited voltage and capacity of individual cells, series and parallel combinations are necessary in practical applications to achieve higher voltage and capacity, thereby meeting the actual power supply requirements of devices.

 

Series Connection of Individual Cells: Voltage is the sum of individual cell voltages, capacity remains unchanged, and internal resistance increases.

 

Parallel Connection of Individual Cells: Voltage remains unchanged, capacity is the sum of individual cell capacities, internal resistance decreases, and power supply duration is extended.

 

Series and Parallel Connection of Lithium Battery Packs: Battery packs incorporate both parallel and series combinations internally, increasing voltage and expanding capacity.

 

Series Voltage:

3.7V individual cells can be assembled into battery packs with voltages of 3.7V × (N)V (where N represents the number of individual cells), such as 3.7V × 2 = 7.4V, 3.7V × 3 = 11.1V, 24V, 36V, 48V, 60V, 72V, etc.

 

Parallel Capacity:

A single 2200mAh battery cell can be assembled into a battery pack with a capacity of 2*(N)mAh (where N represents the number of individual cells), such as:

2*2200mAh = 4400mAh

3*2200mAh = 6600mAh

8*2200mAh = 8800mAh

5Ah, 10Ah, 20Ah, 30Ah, 50Ah, 100Ah, etc.

 

Lithium Battery Pack

Lithium battery PACK refers to the processing, assembly, and packaging of lithium battery packs. The process of assembling lithium battery cells into groups is called PACK. This can involve adding a protection board and wiring to create a single battery, or assembling them into series and parallel lithium battery packs. A lithium battery pack typically consists of a plastic casing, protection board, battery cells, output terminals, connection interfaces, and other components such as insulating tape and double-sided adhesive tape.

 

Components of a Lithium Battery Pack

Lithium Cell: The core component of the finished battery.

Protection Board: Provides intelligent protection functions including overcharge, over-discharge, overcurrent, short-circuit, and NTC temperature control.

Plastic Housing: Supports the entire battery assembly; positions and secures the protection board; accommodates all non-housing components while maintaining dimensional integrity.

Terminal Leads: Provide various terminal connections for charging/discharging interfaces, enabling compatibility with electronic devices, energy storage systems, and backup power solutions.

Nickel Plate/Bracket: Connects and stabilizes the battery cells.

 

Series and Parallel Combination of Lithium Battery Packs

For safety reasons, lithium batteries must be equipped with external protection boards to monitor each cell. Parallel connection is generally not recommended during battery use. If parallel connection is necessary, consistency in all battery parameters (capacity, internal resistance, etc.) must be ensured. Additionally, batteries used in series must also have consistent parameters; otherwise, the performance of the battery pack will be significantly worse than that of individual cells.

 

Lithium battery packs must be connected in series and parallel combinations.

 

The purpose of lithium battery pairing is to ensure that each cell within the battery pack achieves consistent capacity, voltage, internal resistance, and performance. Inconsistencies will cause various parameters within the lithium battery pack to diverge progressively during use, leading to voltage imbalance. Over time, this results in overcharging, over-discharging, and diminished capacity utilization, posing a risk of explosion and fire.

 

Calculation Method for Lithium Battery Series Connection

3-series lithium battery combination (3*3.7V=11.1V lithium battery pack)

4-series lithium battery combination (4*3.7V=14.8V lithium battery pack)

6-series lithium battery configuration (6*3.7V=22.2V lithium battery pack)

 

Lithium Battery Pack Wiring/Terminals

Lithium battery pack connectors and lead lengths can be customized to suit customer's electrical equipment requirements.

 

Calculating Series and Parallel Connections in Lithium Battery Packs

We all know that series connections increase voltage while parallel connections boost capacity in lithium batteries. So how do we determine the number of series and parallel strings, and the total number of cells in a lithium battery pack?

 

Before calculating, we must know the specifications of the cells used in the pack, as different cells have varying voltages and capacities.

 

Assembling a battery pack to specific specifications requires different numbers of series and parallel connections. Common lithium cell types on the market include: - Lithium cobalt oxide (LiCoO₃): 3.7V - Lithium iron phosphate (LiFePO₄): 3.2V - Lithium titanate (LiTiO₃): 2.4V - Lithium manganese oxide (LiMnO₂): 3.6V Capacities vary based on cell size, materials, and manufacturers.

 

For example: 48V 20Ah lithium battery pack

Assuming the individual cell specifications are 18650 3.7V 2000mAh

Number of cells in series: 48V/3.7V = 12.97, resulting in 13 series connections (13 cells in series)

Number of cells in parallel: 20Ah/2Ah = 10, resulting in 10 parallel connections (10 cells in parallel)

The entire battery pack consists of 13 series strings × 10 parallel groups = 130 cells

 

Precautions for Series and Parallel Connection of Lithium Batteries

Do not mix cells from different brands

Do not mix cells with different voltages

Do not mix cells with different capacities or age (new and old)

Do not mix cells with different chemistries, such as nickel-metal hydride and lithium cells

Replace all batteries when the battery pack is low on power

Use a lithium battery protection board with matching specifications

Select batteries with consistent performance; generally, lithium batteries require cell matching when connected in series or parallel

Matching criteria: Voltage difference ≤10mV, Internal resistance difference ≤5mΩ, Capacity difference ≤20mA