Batteries in Parallel vs. Series: What Are the Differences

Solar energy is a clean, sustainable alternative to fossil fuels, but its intermittent nature makes energy storage more important than ever. In home energy systems, batteries store excess solar power generated during the day for use at night or during low-sunlight periods.

This article explores how batteries are connected—whether in series or parallel—highlighting the benefits and drawbacks of each. Understanding this is key to selecting the right configuration for reliable and safe home energy use. 

Batteries in Series

Connecting batteries in series means linking the positive terminal of one battery to the negative terminal of the next. This setup increases the total voltage while keeping the capacity (amp hours, or Ah) the same as a single battery. For example, wiring two 12 V 100 Ah batteries in series gives you 24V at 100 Ah. This is ideal for scenarios that require higher voltage.

System voltage is measured from the free negative terminal of the first battery to the free positive terminal of the last. When charging, use a device that matches the total system voltage.

Connecting Batteries in Series: Pros and Cons

Advantages

• Batteries connected in series offer several benefits, especially when higher voltage is needed for specific applications:
• Increased Voltage: By wiring batteries in series, the voltages add up. This is ideal for powering devices that require more electric force, such as flashlights or motors. 
• Lower Current: The current remains the same as a single battery, which means you can use thinner wires to reduce overall wiring costs and energy loss. 
• Flexible Design Options: Batteries can be arranged in various ways as long as they stay in series, making it easier to design compact or custom systems.
• Simplified Installation: Compared to parallel wiring, series connections usually require fewer cables and are easier to set up, especially in smaller systems.

Disadvantages

While series connections are efficient, they also introduce several challenges and risks:

• Chain Failure Risk: If one battery fails or becomes disconnected, the entire circuit breaks – similar to a broken link in a chain that stops the whole system.
• Increased Electrical Risk: Changing to a higher voltage (e.g., 36 V or 48 V) can pose a threat of greater shock or fire risk, even though these levels are below standard household voltage.
• Strict Matching Requirements: All batteries should be of the same type, voltage, capacity, brand, and resistance, as mismatched batteries can degrade system performance and shorten battery life.

Batteries in Parallel

Connecting batteries in parallel involves linking all the positive terminals and all negative terminals. This setup keeps the system voltage the same as that of a single battery but increases the total Ah capacity. For example, two 12 V, 100 Ah batteries connected in parallel will still output 12 V, but their combined capacity will be 200 Ah. This means the system can supply power at the same voltage for a longer duration, making it ideal for applications requiring extended runtime.

It is critical to use batteries of the same voltage and, preferably, the same capacity, chemistry, and brand to ensure optimal performance. While parallel setups extend usage time, they may take longer to charge due to the larger total capacity. 

Connecting Batteries in Parallel: Pros and Cons

Advantages

• Wiring batteries in parallel increases the total Ah capacity of the system, allowing connected devices to operate for longer periods at a constant voltage. This is ideal for applications that demand extended runtime, such as RVs or energy storage systems.
• One of the biggest strengths of parallel configuration is redundancy. If one battery fails, the others can continue supplying power, minimizing the risk of complete system shutdown.
• Voltage remains consistent across the system. This helps maintain battery health and reduce safety risks compared to series configurations where overall voltage ramps up.

Disadvantages

• Despite the benefits, there are some challenges to consider when wiring batteries in parallel.
• Balancing issues may occur if the batteries are not closely matched in capacity, voltage, age, or internal resistance. This can lead to one battery discharging into another to “equalize” the voltage, causing energy loss or potential damage.
• A more sophisticated charging system may be needed to ensure all batteries are charged evenly, particularly in large systems.
• As more batteries are added, they must be closely positioned, which may be a concern in space-constrained environments.
• There's also a risk of thermal runaway. If one battery overheats, the heat can spread to others, especially in tightly packed configurations.

FranklinWH aPower 2: Up to 15 Batteries in Parallel Per aGate for the Most Advanced Energy Needs

FranklinWH offers an innovative home energy management and battery storage system that allows people to generate, store, and intelligently manage their home energy, optimizing clean energy use and reinforce energy security.

The FranklinWH aPower 2 battery provides an impressive 15 kWh of storage capacity per unit. If a homeowner’ energy demand significantly grows, capacity can be easily expanded by adding more batteries, achieving a total storage capacity of up to 225 kWh (15 units) per aGate controller.

Every aPower 2 battery comes equipped with a built-in inverter, enabling each unit to independently manage its charging-discharging level, eliminating issues related to uneven charging or discharging. 

Additionally, each aPower 2 battery has a sophisticated Battery Management System (BMS) that closely monitors temperature, voltage, and current in real-time. This ensures each battery remains thermally stable, actively preventing overheating and safeguarding your entire energy management and storage system.

Conclusion

Series connections are ideal for higher voltage applications, while parallel configurations provide extended runtime and increased redundancy, making them suitable for applications requiring longer power duration. For homeowners with advanced energy needs, the FranklinWH aPower 2 offers a flexible solution, allowing up to 15 units to be connected in parallel per aGate for a substantial capacity. With a built-in inverter and an advanced BMS, the aPower 2 ensures exceptionally reliable and safe performance when you expand your system, making it a perfect choice for residential energy storage.