The Impact of Series and Parallel Connections of Battery Cells on the Performance Parameters of Drone Batteries

Drone Battery

ENOV High-Energy drone batteries power industrial and commercial drones. Delivering 220–320 Wh/kg energy density, they enable long flight times (30+ mins) and support fast charging (2C). Perfect for aerial photography, surveillance, and delivery drones.

The core performance parameters of drone batteries, such as voltage, capacity, and discharge capability, are entirely determined by the series (abbreviated as “S”) and parallel (abbreviated as “P”) combinations of battery cells. These two connection methods directly affect the drone’s take-off capability, flight duration, power output, and flight safety by altering the key characteristics of the battery cells. The following is a detailed analysis from the perspectives of the individual effects of series and parallel connections, the logic of series-parallel combinations, the comprehensive impacts, and practical precautions.

1. Series Connection of Battery Cells: Core Impact on Voltage, Determining the Power Foundation of Drones

Series connection refers to connecting multiple battery cells in sequence following the “positive electrode to negative electrode” order. Its essence is “voltage superposition, constant capacity, and constant discharge capability”. It is the basic configuration to meet the high-voltage demand of drone motors. Common 4S and 6S batteries are all designed based on series connection.

(1) Specific Impacts on Battery Performance Parameters

Voltage: The total voltage increases linearly with the number of cells in series, and the total voltage is equal to the voltage of a single cell multiplied by the number of series-connected cells. The nominal voltage of lithium-polymer cells commonly used in drones is 3.7V. Therefore, the total voltage of 3 series-connected cells (3S) is 11.1V, that of 4 series-connected cells (4S) is 14.8V, and that of 6 series-connected cells (6S) is 22.2V.

Capacity: The total capacity is the same as that of a single cell and does not change with the increase in the number of series-connected cells. For example, after 2 cells of 2000mAh are connected in series, the total capacity remains 2000mAh; when 5 cells of 5000mAh are connected in series, the total capacity is still 5000mAh.

Current Capability: The maximum discharge current remains at the level of a single cell and does not increase due to the series connection. If the maximum discharge current of a single cell is 10A, even if multiple cells are connected in series, the total maximum discharge current is still 10A. However, the total power will increase with the rise in voltage (Power = Voltage × Current).

Discharge Rate (C-Rate): The discharge rate is determined by the performance of a single cell, and the overall discharge rate remains unchanged after series connection. If a single cell supports a 10C discharge rate, the battery pack after series connection still maintains a 10C discharge capability.

Flight Duration: Since the capacity does not change, the flight duration is not directly improved. The final flight duration needs to be comprehensively determined based on the actual power consumption of the drone and the battery capacity.

Weight and Volume: The weight and volume increase linearly with the number of series-connected cells. Each additional cell will cause the weight and volume of the battery to increase simultaneously, while the overall energy density remains basically unchanged (Energy = Voltage × Capacity, Density = Energy / Weight; since voltage is proportional to weight, the ratio remains stable).

Safety: The safety requirements are significantly enhanced. In the case of a series connection, if the consistency of the cells is poor (such as deviations in voltage, internal resistance, and capacity), some cells may be fully charged first during charging, leading to overcharging, and some cells may be drained first during discharging, resulting in over-discharging. These situations are prone to causing risks such as cell bulging and fire. Therefore, a Battery Management System (BMS) must be equipped for balanced management to monitor the status of each cell.

(2) Practical Effects on Drones

Determining Normal Startup: The core components of a drone, such as the motor and flight controller, have fixed voltage requirements. For example, the DJI Mini series requires a 3S battery (11.1V), and the Inspire series requires a 6S battery (22.2V). An insufficient number of series-connected cells will lead to low voltage, making the equipment unable to start; an excessive number of series-connected cells will cause high voltage, directly burning the circuit.

Affecting Power Upper Limit: With the same capacity, the more the number of series-connected cells (the higher the voltage), the greater the power the battery can provide to the motor. This enables the drone to achieve faster acceleration, higher flight speed, or carry heavier loads (such as professional aerial cameras).

2. Parallel Connection of Battery Cells: Core Impact on Capacity and Current, Determining the Flight Duration and Heavy-Load Capability of Drones

Parallel connection refers to connecting multiple battery cells in the way of “positive electrode to positive electrode and negative electrode to negative electrode”. Its essence is “capacity superposition, current capability superposition, and constant voltage”. It is mainly used to improve the battery’s flight duration and high-load discharge capability, but a large parallel structure with more than 2P is rarely used in drones.

(1) Specific Impacts on Battery Performance Parameters

Voltage: The total voltage is exactly the same as that of a single cell and does not change with the increase in the number of parallel-connected cells. No matter how many 3.7V cells are connected in parallel, the total voltage is always maintained at 3.7V, and it needs to be combined with series connection to meet the high-voltage demand of the drone.

Capacity: The total capacity increases linearly with the number of parallel-connected cells, and the total capacity is equal to the capacity of a single cell multiplied by the number of parallel-connected cells. For example, after 2 cells of 2000mAh are connected in parallel, the total capacity is 4000mAh; when 3 cells of 5000mAh are connected in parallel, the total capacity can reach 15000mAh.

Current Capability: The maximum discharge current is superimposed with the number of parallel-connected cells, and the total discharge current is equal to the maximum discharge current of a single cell multiplied by the number of parallel-connected cells. If a single cell supports a 10A discharge current, the total discharge current of 2 parallel-connected cells is 20A, and that of 3 parallel-connected cells is 30A, which can better meet the current demand of the drone in high-load scenarios.

Discharge Rate (C-Rate): The actual discharge rate will “decrease”. After the capacity is increased, under the same discharge current, the C-rate (discharge current / capacity) will decrease accordingly, reducing the battery’s discharge pressure and making the working state more stable. For example, a single 2000mAh cell discharges at 10A (5C); after 2 cells are connected in parallel, the capacity is 4000mAh, and the discharge at the same 10A is only 2.5C.

Flight Duration: The flight duration is significantly improved. The total energy of the battery = Voltage × Capacity. The increase in capacity directly improves the total energy. Under the condition of fixed power consumption of the drone, the flight duration will be extended proportionally with the increase in capacity. For example, a 3S 5000mAh battery (Energy = 11.1V × 5Ah = 55.5Wh) has a 60% longer flight duration than a 3S 3000mAh battery (33.3Wh).

Weight and Volume: The weight and volume increase with the number of parallel-connected cells. Moreover, due to the need for additional connection structures, the energy density will decrease slightly, but the overall impact is small.

Safety: There is a risk of circulation current. If the consistency of the parallel-connected cells is poor (such as voltage difference), the cell with higher voltage will charge the cell with lower voltage in the reverse direction at the moment of power-on, generating a large current, which may burn the connection point or cause heat damage. Therefore, strict matching of the cells or isolation design must be adopted.

(2) Practical Effects on Drones

Extending Flight Duration: It is suitable for scenarios where long flight duration is required, such as fixed-wing drones and agricultural plant protection drones. The capacity is increased by increasing the number of parallel-connected cells to meet the demand for long-term operations.

Improving Heavy-Load and High-Load Capabilities: When the drone takes off, hovers, flies at high speed, or carries heavy objects, the motor needs a larger instantaneous discharge current. If the discharge capability of a single cell is insufficient, it will lead to insufficient power supply, resulting in motor power attenuation, altitude drop, or even crash. After parallel connection, the discharge current is superimposed, which can meet the high-load demand and ensure stable flight.

(3) Reasons Why Large Parallel Structures Are Rarely Used in Drones

The requirement for cell consistency is extremely high. It is necessary to ensure that the capacity, internal resistance, and voltage of the cells are completely matched, resulting in high screening costs.

The problem of circulation current is difficult to completely avoid, which is prone to causing safety hazards and increasing maintenance difficulty.

An excessive number of parallel-connected cells will lead to a significant increase in battery weight, which in turn increases the flight power consumption of the drone and partially offsets the benefits of extended flight duration.

3. Series-Parallel Combination: Balancing Voltage, Capacity, and Current to Adapt to Different Drone Scenarios

Practical drone batteries all adopt the “series + parallel” combination method (such as 6S1P, 4S2P, 3S2P, etc.). The core logic is to “use series connection to meet the voltage demand and parallel connection to meet the capacity and discharge demands”. Different combinations correspond to the performance requirements of different drones.

(1)Common Combinations and Application Scenarios

Combination Mode	Assumed Parameters of Single Cell	Total Voltage	Total Capacity	Total Discharge Current (Taking 20 Casan Example)	Adapted Drone Type	Adaptation Logic
6S1P	3.7V/2200mAh	22.2V	2200mAh	88A	Racing drones, medium-sized drones	High voltage provides strong power to meet the demand for high-speed flight; single parallel connection (1P) controls weight to ensure flight flexibility
4S2P	3.7V/2000mAh	14.8V	4000mAh	80A	Long-endurance drones, low-power models	Medium voltage balances power and power consumption; dual parallel connection (2P) increases capacity and extends flight duration, adapting to long-term operation scenarios
3S2P	3.7V/5000mAh	11.1V	10000mAh	200A	Consumer aerial photography drones (e.g., DJI Air series)	Moderate voltage adapts to mainstream motors; dual parallel connection (2P) balances high capacity (long flight duration) and high discharge capability, meeting the needs of daily aerial photography
4S3P	3.7V/4000mAh	14.8V	12000mAh	240A	Professional aerial photography drones (e.g., DJI Inspire series)	Higher voltage ensures strong power and supports mounting professional equipment; triple parallel connection (3P) increases capacity and discharge current, balancing flight duration and heavy-load demands

(2) Core Principles of Combination Design

Voltage Priority: First, determine the number of series-connected cells according to the rated voltage of the drone’s motor and flight controller. For example, if the motor requires 11.1V, 3S series connection is preferred; if the motor is adapted to 14.8V, 4S series connection is determined.

Capacity and Discharge Adaptation: Then, determine the number of parallel-connected cells based on the flight duration requirement (capacity) and flight load (discharge current). If long flight duration is needed, increase the number of parallel-connected cells; if heavy load carrying or high-speed flight is required, improve the discharge capability through parallel connection.

Safety Restrictions: The more the number of series or parallel-connected cells, the higher the requirement for cell consistency. Cells of the same brand, model, and batch should be selected, and a BMS should be equipped to monitor the status of each cell in real time to avoid overcharging and over-discharging.

4.Summary of the Comprehensive Impacts of Series and Parallel Connections on Drone Battery Performance

Performance Parameter	Impact of Series Connection	Impact of Parallel Connection
Voltage	Increased	Unchanged
Capacity	Unchanged	Increased
Flight Duration	Not directly improved	Significantly improved
Maximum Current Output	Unchanged	Increased
Power Output	Increased (voltage increases, current remains unchanged)	Increased (current increases, voltage remains unchanged)
Weight/Volume	Increased	Increased
Safety Requirements	BMS balanced management required	Circulation current prevention design required
Cell Consistency Requirement	High	Higher

5. Practical Suggestions and Key Precautions

(1) Battery Selection for Different Types of Drones

Multi-rotor Drones: Priority is given to the combination of “high voltage + medium capacity”, such as 6S1P and 4S1P. Reducing the number of parallel-connected cells can reduce the risk of circulation current, and high voltage ensures power, adapting to the flexible flight demand.

Fixed-Wing/Long-Endurance Drones: The combination of “medium voltage + multiple parallel connections” can be selected, such as 4S2P and 3S2P. On the premise of meeting the basic power, the capacity is increased through parallel connection to extend the flight time.

Racing/Heavy-Load Drones: The combination of “high voltage + appropriate parallel connections” is selected, such as 6S2P and 4S3P. High voltage provides strong power, and appropriate parallel connections improve the discharge current to meet the current demand of high-speed or heavy-load scenarios.

(2) Key Precautions

Mixing of Old and New Cells Is Strictly Prohibited: There are large differences in capacity, internal resistance, and voltage between old and new cells. Mixing them will cause some cells to be overcharged or over-discharged, leading to heat generation, bulging, and even crash accidents. Cells of the same batch and with the same parameters must be used.

Pay Attention to Discharge Rate (C-Rate) Matching: The continuous discharge C-rate of the battery must be greater than the maximum current demand of the drone. If the C-rate is insufficient, the voltage will drop sharply when the motor is under high load, triggering flight controller protection (forced landing). It is necessary to select a battery with an appropriate C-rate according to the flight scenario (e.g., a C-rate of 30C or above for racing drones, and a C-rate of 20-25C for consumer aerial photography drones).

Balance Energy Density and Weight: The more the number of parallel-connected cells, the higher the capacity, but the battery weight also increases accordingly, which may increase the flight power consumption of the drone, resulting in the range of flight duration being lower than that of capacity. It is necessary to select a battery with the optimal “capacity-weight ratio” based on the Maximum Take-Off Weight (MTOW) of the drone.

Attach Importance to BMS Function: Multi-series or multi-parallel batteries must be equipped with a qualified BMS, which can monitor the voltage and temperature of each cell in real time, prevent overcharging, over-discharging, and overcurrent, and is a core component to ensure battery safety. It is necessary to confirm that the BMS function is intact when purchasing.