Batteries in Series vs Parallel: Understanding the Key Differences

In the application of batteries, series connection (Series) and parallel connection (Parallel) are two basic and vital connection methods. They each have unique characteristics and advantages, and are suitable for different scenarios and needs. In this article, we will discuss the difference between series and parallel connection of batteries and answer the question of how to properly select and implement these two connection methods.

Basic Concepts of Batteries

A battery is a device that converts chemical energy into electrical energy by generating an electric current through an internal chemical reaction to provide electrical power to external devices. Batteries are usually composed of a positive electrode, a negative electrode, an electrolyte and a case, among which the positive and negative electrodes are the core parts of the battery, which exchange ions through the electrolyte to produce an electric current. There are many types of batteries, according to the type of electrolyte can be divided into alkaline batteries, acid batteries, organic electrolyte batteries, etc.; according to whether the rechargeable can be divided into primary and secondary batteries; according to the use can be divided into dry cell batteries, storage batteries, fuel cells and so on.

Core Parameters of a Battery

Understanding these core parameters is critical to the selection and use of batteries, as well as understanding that the series and parallel connection of batteries affects the performance of the battery pack by influencing the values of the battery's core parameters

Battery Capacity

Battery capacity refers to the amount of electricity that a battery can release under specific conditions, usually expressed in terms of ampere-hours (Ah) or milliampere-hours (mAh). Battery capacity is directly related to the amount of active material inside the battery and is also affected by the material and volume of the battery. The higher the capacity, the more power the battery can store and the longer it can supply power without recharging. For example, a battery with a capacity of 2000mAh can theoretically supply power for up to 1 hour at 2000mAh.

Nominal Voltage

Nominal voltage refers to the potential difference between the positive and negative terminals of the battery when it is shipped from the factory. It reflects the voltage level of the battery during normal operation and is usually closely related to the chemistry of the battery. Nominal voltage is an important indicator for evaluating the suitability of a battery for a particular device. For example, common AA alkaline batteries have a nominal voltage of 1.5 volts, while lithium-ion batteries typically have a nominal voltage of 3.7 volts. Different types of batteries have different nominal voltages and should be selected to ensure that they match the voltage requirements of the equipment in which they will be used.

Internal Resistance

Internal resistance refers to the obstruction of current flow inside the battery, which consists of plate resistance and ion flow impedance. The size of internal resistance has an important effect on the discharge performance and charging efficiency of the battery. The smaller the internal resistance, the less power loss the battery has during discharge, and the better the discharge performance. At the same time, a smaller internal resistance will also improve the charging efficiency of the battery. Internal resistance is often expressed in milliohms (mΩ), and higher internal resistance can cause the battery to overheat and affect its service life.

When designing a battery pack, the core parameters of the entire battery pack are formally influenced by connecting the cells in series or parallel to meet the needs of the application scenario. Read more about series and parallel connection of batteries below.

Series connection of batteries

Battery series connection refers to connecting the positive and negative terminals of multiple batteries in sequence to form a continuous current path. The main feature of this type of connection is the ability to increase the total voltage of the battery pack, while the current output capability remains essentially unchanged. The total voltage of a series-connected battery pack is equal to the sum of the voltages of the individual cells, making it ideal for applications where high voltage output is required (e.g., electric vehicles, high-voltage lamps, etc.).

For example, if you connect three batteries of 1.5 volts each in series, the overall system voltage will be 4.5 volts.

How to connect batteries in series

The steps for connecting batteries in series are as follows:

• Prepare the materials: prepare the batteries to be connected in series and the appropriate connecting wires.
• Connect the batteries: connect the positive terminal of the first battery to the negative terminal of the second battery, the positive terminal of the second battery to the negative terminal of the third battery, and so on.
• Measure the total voltage: After the connection is complete, use a multimeter to measure and confirm the total voltage of the entire battery pack.

Battery Parallel Connection Explained

In contrast to series connections, battery parallel connections are made by connecting the positive terminals of multiple batteries all together and the negative terminals all together to share the current. The main advantage of connecting in parallel is the ability to increase the total current output capacity of the battery pack while keeping the voltage constant. This makes parallel battery packs very useful in situations where a high current supply is required (e.g., starting high-power devices, emergency power, etc.).

For example, if you have three batteries, each of which is 12 volts, when connected in parallel, the voltage will still be 12 volts, but the capacity will be the sum of the individual battery capacities.

How to connect batteries in parallel

The steps for connecting batteries in parallel are as follows:

• Prepare materials: make sure you have multiple batteries of the same voltage and connecting wires.
• Connect the batteries: Connect the positive terminals of all the batteries together through the wires and the negative terminals are also connected.
• Measure total capacity: After connecting in parallel, use a multimeter to confirm that the voltage remains constant and calculate the total capacity of the system.

Advantages and disadvantages of connecting batteries in series and parallel

Advantages and disadvantages of connecting batteries in series

Advantages

• Increased voltage: The total voltage of a series battery pack is equal to the sum of the individual cell voltages, which makes the series method ideal for applications that require high voltage, such as drones and power tools.
• Space efficient: Series battery packs typically take up less space than parallel designs because no additional wiring and equipment is required.
• Relatively low cost: for the same voltage requirement, series battery packs may require fewer cells, which reduces the overall cost.

Disadvantages

• Capacity limitations: Series battery packs have the same capacity as individual cells, which limits their ability to supply power for long periods of time.
• Risk of single point of failure: If one cell in a series battery pack fails, the entire system will fail, increasing the vulnerability of the system.
• High demand for battery consistency: The batteries in a series battery pack need to be of the same type and age to ensure consistent performance. If the batteries are not consistent, it may lead to voltage imbalance and affect the overall performance.
• High BMS requirements: Series battery packs require a more sophisticated battery management system (BMS) to monitor and control the status and performance of each cell to ensure stable system operation.

Advantages and disadvantages of parallel connection of batteries

Advantages

• Increased capacity: The total capacity of a parallel battery pack is equal to the sum of the individual cells' capacities, providing a longer operating time.
• Equalized Charging: In a parallel battery pack, each cell is charged at the same rate, which helps maintain consistency and longevity.
• Redundancy: If one battery is depleted or fails, the others can continue to supply power, ensuring continuous system operation.
• Ease of Maintenance: Cells in a parallel battery pack can be more easily replaced or maintained individually.

Disadvantages

• Constant voltage: The total voltage of a parallel battery pack is the same as the voltage of the individual cells, which is not suitable for application scenarios that require high voltage.
• Potentially higher energy consumption: Due to the higher current, the energy consumption of a parallel battery pack is relatively high, which may lead to a decrease in system efficiency.
• Current distribution problems: If the cells are mismatched or improperly connected, this may lead to uneven current distribution and affect the overall performance of the battery pack.

Comparative analysis of batteries in series and parallel

How to choose whether to connect batteries in series or in parallel

When choosing whether to connect batteries in series or in parallel, the decision needs to be based on a combination of specific application requirements, battery performance parameters, and system design. Here are some key considerations:

1. Voltage Requirements

• Series connection: If the equipment requires a higher voltage, and the voltage of a single battery can not meet the requirements, the series connection should be selected. The total voltage of the series-connected battery pack is equal to the sum of the individual battery voltages, which can satisfy the application scenarios with high voltage requirements, such as drones and electric vehicles.
• Parallel connection: If the equipment does not have special requirements for voltage, or the voltage of individual batteries already meets the demand, but need a higher current or longer use time, then you can consider the parallel connection method. The total voltage of the parallel battery pack is the same as that of a single battery, but the total current and capacity will be increased.

2. Current and Capacity Requirements

• Series connection: The current of series connection battery pack is the same as individual battery, but the capacity is also the same. If you need to supply power for a long time, but the current demand is not big, you can extend the use time by increasing the number of series-connected batteries (in the case of the load current remains unchanged).
• Parallel: The total current of a parallel battery pack is equal to the sum of the branch currents, and the total capacity is equal to the sum of the individual battery capacities. Therefore, when the equipment requires high current output or longer duration, parallel connection is more appropriate. For example, electric motors, mobile communication base stations and other applications often use parallel battery packs.

3. System Stability and Reliability

• Series: The voltage provided by series battery packs is more stable because the current passes through the cells sequentially without shunting. However, there is a single point of failure risk in series battery packs, once a battery cell fails, the whole system will be affected. As a result, there is a high demand for battery consistency and a complex battery management system (BMS) is required to monitor and control the status of each cell.
• Parallel: A parallel battery pack has redundancy, so even if one battery fails, the others can continue to supply power, improving system reliability. However, parallel battery packs also have certain requirements on the consistency of the batteries to avoid performance degradation caused by uneven current distribution.

4. Space and Cost Considerations

• Series: Series battery packs are usually more efficient in terms of space utilization, as no additional connecting wires and equipment are required. In terms of cost, if the voltage requirements are the same, a series battery pack may require fewer cells, thus reducing costs.
• Parallel: Parallel battery packs require more cells and connecting wires and therefore may cost more. However, in application scenarios that require high current or long range, parallel connection may be a more economical choice.

5. Comprehensive selection recommendations

• Define the needs: First define the specific needs of the device for voltage, current, capacity and range.
• Evaluate battery performance: Consider factors such as battery type, voltage, capacity and consistency.
• Consider system design: Conduct a comprehensive evaluation based on factors such as equipment design requirements, space constraints and maintenance convenience.
• Cost-benefit analysis: Compare the advantages and disadvantages of series and parallel connection methods in terms of cost, performance and reliability, and select the most suitable solution.

To summarize, choosing whether to connect batteries in series or in parallel requires comprehensive consideration based on specific application scenarios and needs. In practical applications, the performance of different connection methods can be verified through tests and simulations to make a more informed choice.

Battery Connection Methods for Common Application Scenarios

Batteries are often connected in different ways (series or parallel) in different application scenarios, depending on the needs. The following are some common application scenarios and their connection methods:

1. Mobile electronic devices

• Application scenarios: cell phones, tablet PCs, laptops, etc.
• Connection method: Usually parallel connection is used. The reason is that these devices have a high demand for battery capacity and need to provide a longer usage time, while the voltage is usually provided by a single or a small number of batteries, so the parallel connection can increase the total capacity and keep the voltage stable.

2. Electric Vehicles

• Application Scenario: Electric passenger cars, buses, etc.
• Connection method: usually series connection. Electric vehicles require higher operating voltage to increase power output, so multiple batteries are connected in series to achieve the required high voltage. At the same time, the battery pack of an electric vehicle will usually consist of multiple individual batteries, and within each pack, they may also be connected in parallel to increase the total capacity.

3. Solar Energy Storage Systems

• Application scenarios: home solar energy storage, grid energy storage.
• Connection method: Usually a combination of series and parallel connection is used. The voltage of the battery pack is increased by series connection to match the voltage demand of the inverter or other equipment, while the overall capacity is increased by parallel connection to ensure that enough energy can be stored.

4. Electric tools

• Application Scenario: Electric drills, saws and other power tools.
• Connection: Most power tools are connected in series. Because these tools often require high starting currents, they are connected in series to obtain enough voltage to drive the motor.

5. Drones

• Application scenarios: consumer and industrial drones.
• Connection: Usually connected in parallel. Drones need long endurance and high current for short periods of time to cope with acceleration and climb, so multiple batteries are connected in parallel to increase capacity while keeping the device lightweight.

6. Backup power systems

• Application scenarios: uninterruptible power supply (UPS), emergency lighting.
• Connection: Usually connected in parallel. Backup power systems need to provide a lasting supply of power in the event of a power outage, so multiple batteries are connected in parallel to provide greater capacity and ensure a reliable continuation of the power supply.

7. Portable charging equipment

• Application scenarios: mobile power, portable chargers.
• Connection: Generally connected in parallel. In order to meet the demand for multiple charging, portable chargers often use parallel connection to increase capacity, thus improving their charging capability.

FAQs

What is the biggest disadvantage of series-connected batteries?

The biggest disadvantage of a series battery system is that the performance of the entire system is limited to the weakest battery.

Do I need to use the same brand or model of batteries for parallel connection?

Yes, it is recommended to use the same brand and type of batteries to ensure that the performance of each battery is matched. 

What happens if one of the cells in a series battery pack goes bad?

If one of the batteries in a series battery pack goes bad, the entire system will not work.

Can a parallel battery pack provide a higher voltage?

No. The voltage of a parallel battery pack is equal to the voltage of the individual cells and will not increase.

How do I calculate the voltage and capacity of a series or parallel battery pack?

The total voltage of a series battery pack is the sum of the voltages of the individual cells, and the capacity remains constant; the total capacity of a parallel battery pack is the sum of the capacities of the individual cells, and the voltage remains constant.

Is it better to connect batteries in series or in parallel?

The choice of connecting batteries in series or parallel is not absolute, but depends on the specific application scenario and requirements.

• Series connection: Suitable for devices that require high voltage but not much current demand, such as drones and electric vehicles. Series connection can increase the total voltage of the battery pack so that the equipment can work normally.
• Parallel connection: suitable for devices that require high current output or long time power supply, such as electric vehicles, energy storage systems, mobile communication base stations and so on. Parallel connection can increase the total current and total capacity of the battery pack and extend the range time of the equipment.

Therefore, it is not possible to simply say whether it is better to connect batteries in series or in parallel, but rather the choice needs to be based on actual needs.

Which is more efficient, batteries in series or parallel?

Ideally, a parallel-connected battery pack usually has a higher energy conversion efficiency due to lower internal resistance. However, in practice, an uneven distribution of current between parallel-connected batteries may result in overloading or overheating of some batteries, which reduces overall efficiency. In contrast, the efficiency of series-connected battery packs may be affected by cell consistency, internal resistance, and other factors, but they typically provide a more stable voltage output.

Which lasts longer, series or parallel?

Under the same load conditions, parallel-connected battery packs typically have a longer range due to their greater total capacity. The duration of a series battery pack, on the other hand, depends on the capacity and duration of use of the individual cells. Therefore, in application scenarios where power is required for a long period of time, parallel battery packs may be more advantageous.

Which is safer, series or parallel?

Regarding safety, batteries connected in parallel and in series each have their own potential risks.

• Series: Failure of a single cell in a series-connected battery pack can result in a large change in the voltage of the entire system, which can easily lead to overheating or even explosion of the batteries. In addition, differences in battery life and unbalanced charging and discharging may also lead to safety hazards.
• Parallel connection: Although parallel connection of battery packs can ensure voltage balance, it may also lead to overloading, overheating or even fire if the current between cells is not evenly distributed or managed properly.

Therefore, whether connected in series or parallel, appropriate safety measures and management strategies are required to ensure the safe operation of the battery pack. When selecting, the safety requirements of the equipment, battery performance parameters and the comprehensive factors of system design should be taken into account.