Understanding Battery Pack Configurations: Series vs. Parallel Explained

by Mike Beard in Battery Knowledge Base

Battery pack configurations determine how much power a battery can provide and for how long. Whether you're choosing a battery pack for an electric vehicle, a robotics project, or an energy storage system, understanding the difference between series and parallel connections can help you make the best decision.

Series Connection: Increasing Voltage

How It Works

Think of series connection like stacking batteries in a flashlight. When you place batteries end-to-end, the voltage adds up, giving more power to the device. However, while the total capacity in terms of amp-hours (Ah) remains the same as one battery, the total energy stored, measured in watt-hours (Wh), does increase since watt-hours depend on both voltage and capacity.

Formula:

  • Total Voltage (V) = Sum of Individual Cell Voltages

  • Total Capacity (Ah) = Same as a Single Cell

  • Total Current Output (A) = Same as a Single Cell

Example: 2S1P Configuration

If you connect two 3.6V Li-ion cells (each 4200mAh) in series:

  • Total Voltage = 7.2V (3.6V × 2)

  • Total Capacity = 4200mAh (Same as a single cell)

  • Total Current Output = 40A (Same as a single cell)

This means the battery pack can power a device that requires 7.2V but will last as long as a single 4200mAh battery before needing a recharge.

Parallel Connection: Increasing Capacity and Current Output

How It Works

Parallel connection is like adding multiple fuel tanks to a vehicle. Each additional tank increases the total amount of fuel available, allowing the vehicle to travel longer distances and deliver more power when needed. Similarly, each added battery in parallel increases the total energy storage and allows the battery pack to deliver more current to high-power devices.

Formula:

  • Total Voltage (V) = Same as a Single Cell

  • Total Capacity (Ah) = Sum of Individual Cell Capacities

  • Total Current Output (A) = Sum of Individual Cell Currents

Example: 1S2P Configuration

If you connect two 3.6V Li-ion cells (each 4200mAh) in parallel:

  • Total Voltage = 3.6V (Same as a single cell)

  • Total Capacity = 8400mAh (4200mAh × 2)

  • Total Current Output = 80A (40A × 2)

This means the battery pack can power a 3.6V device for twice as long as a single cell and supply twice the current for high-power applications.

Combining Series and Parallel (S-P Configuration)

Many battery packs combine series and parallel connections to get the best of both worlds—higher voltage and longer battery life.

Example: 2S2P Configuration

If you connect four 3.6V Li-ion cells (each 4200mAh) in a 2S2P configuration:

  • Total Voltage = 7.2V (3.6V × 2 in series)

  • Total Capacity = 8400mAh (4200mAh × 2 in parallel)

  • Total Current Output = 80A (40A × 2 in parallel)

This setup can power a 7.2V device and last twice as long as a single 4200mAh cell while also handling higher current loads.

Calculating Watt-Hours (Wh)

How It Works

Watt-hours (Wh) measure the total energy stored in a battery pack. This is calculated by multiplying the total nominal voltage (V) by the total capacity (Ah). This value helps determine how long a battery can power a device.

Formula:

  • Watt-Hours (Wh) = Voltage (V) × Capacity (Ah)

Example Calculations:

  • 2S1P Configuration:

    • Voltage = 7.2V (3.6V × 2 in series)

    • Capacity = 4.2Ah (4200mAh converted to Ah)

    • Total Energy = 30.24Wh (7.2V × 4.2Ah)

  • 1S2P Configuration:

    • Voltage = 3.6V

    • Capacity = 8.4Ah (4200mAh × 2 in parallel)

    • Total Energy = 30.24Wh (3.6V × 8.4Ah)

  • 2S2P Configuration:

    • Voltage = 7.2V (3.6V × 2 in series)

    • Capacity = 8.4Ah (4200mAh × 2 in parallel)

    • Total Energy = 60.48Wh (7.2V × 8.4Ah)

Choosing the Right Configuration

  • Use Series Configuration if you need a higher voltage for motors, power tools, or other high-power applications.

  • Use Parallel Configuration if you need a longer runtime for devices like energy storage systems and backup power supplies.

  • Use a Combined S-P Configuration when both higher voltage and extended capacity are required.

Conclusion

Battery pack configurations affect how much power your device gets and how long it lasts. Whether you need more voltage, longer runtime, or both, knowing how batteries are connected helps you pick the right pack. If you need help choosing the best battery for your project, our team is here to assist!

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