What is a Series Connection? 

A series connection is used when you need to increase the total voltage of your battery system while keeping the capacity (amp-hours) the same and doubling the watt-hours (Wh). 

To connect batteries in series, the positive terminal of one battery is connected to the negative terminal of the next. The remaining open terminals (one negative and one positive) become the new connection points for the system. 

For example, if you connect two 12V 100Ah batteries in series: 

• The voltage increases to 24V (12V + 12V). 
• The capacity stays at 100Ah. 
• The watt hours (Wh) are doubled.  

This means that while the system has a higher voltage, the total amount of stored energy (watt-hours) remains the same. 

Why Use a Series Connection? 

Higher voltage is useful in systems that require more efficient power delivery, especially for larger inverters, heavy-duty appliances, or long-distance cable runs. Here are some of the main benefits of series connections. 

More Efficient Power Transmission 

Higher voltage allows power to be transmitted more efficiently over longer distances. This is because increasing the voltage reduces the current draw, which in turn minimises energy loss due to resistance in the wiring. 

Essential for Some Inverters and Appliances 

Many high-power inverters and appliances require 24V or 48V to operate efficiently. If you are running a large off-grid system with a high-power inverter, a series connection may be necessary to meet the voltage requirements. 

Allows Use of Thinner Cables 

Since higher voltage reduces current draw, series connections can sometimes allow for the use of thinner cables compared to an equivalent system running at 12V. This can be particularly useful in systems where wiring runs over long distances. 

Series vs Parallel: What’s the Difference? 

Series and parallel connections serve different purposes, so it’s important to understand which one suits your setup best. 

• Series connection increases voltage while keeping the capacity (Ah) the same. 
• Parallel connection increases capacity (Ah) while keeping the voltage the same. 
• In both configuration, the Wh are increased. 

For example: 

• Two 12V 100Ah batteries in series = 24V 100Ah. 
• Two 12V 100Ah batteries in parallel = 12V 200Ah. 

If your system is designed for 12V appliances, a parallel connection is typically the best choice, as it provides more stored energy without increasing voltage. However, if you need a higher voltage system, a series connection is required. 

Best Practices for Connecting Batteries in Series 

While connecting batteries in series is straightforward, there are a few key guidelines to follow to ensure safety, efficiency, and long-term reliability. 

Use Identical Batteries 

Always use batteries that are the same voltage, capacity, type, and age. Mixing different batteries can lead to imbalances, reduced performance, and even damage to the batteries. 

Ensure Proper Cable Sizing 

Even though series connections reduce current draw, you still need to use properly sized cables rated for the expected load. Undersized cables can create voltage drops, overheating, and inefficiency in your system. It’s also important that all linking cables are exactly the same size.   

Charge Batteries as a Single Bank 

When charging batteries in series, you need a charger that matches the total system voltage. For example, if you have two 12V batteries in series (24V total), you need a 24V charger to ensure proper charging. Charging each battery separately can cause imbalances over time. 

Top balancing the batteries before series connection 

It’s important to top balance all batteries individually before they are connected together. This ensures all batteries will discharge and charge at a uniform rate once the parallel bank is connected. Failing to do so will result in the batteries discharging at varying rates, resulting in reduced battery life and potentially battery failures. 

Balance the System Load 

When wiring appliances or an inverter to a series battery bank, connect the load evenly across the system. This prevents excessive strain on one battery and ensures even discharge across the entire system. 

Use a Battery Management System (BMS) for Lithium
Batteries 

If you are using lithium batteries, a BMS (Battery Management System) is essential. It prevents overcharging, over-discharging, and temperature-related damage, ensuring your batteries remain in peak condition. 

Common Mistakes to Avoid 

While a series connection is simple to set up, there are a few pitfalls to watch out for. 

• Mixing different batteries – Using batteries of different voltages, capacities, or chemistries can cause serious performance issues and shorten battery life. 
• Using an incorrect charger – A charger that doesn’t match the total voltage of your system won’t charge the batteries correctly, leading to imbalances or undercharging. 
• Connecting 12V appliances to a series bank – If you connect a 12V appliance directly to a 24V or 48V series battery bank, you could damage the appliance. A DCDC voltage converter is required to step the voltage down for 12V devices. 
• Not monitoring battery health – Regularly check voltage levels and battery performance to ensure everything is running smoothly. 

When Should You Use a Series Connection? 

A series connection is ideal in situations where a higher voltage is required. Some common use cases include: 

• Running a 24V or 48V off-grid solar system with high-power appliances. 
• Operating large inverters that require more than 12V to function. 
• Reducing power loss in long cable runs where lower voltage would result in significant resistance and inefficiency. 
• Setting up electric vehicles or industrial power systems that need higher voltage for better performance. 

For most camping and 4WD applications, a parallel connection is more common, as it increases power storage without changing the voltage. However, for larger off-grid setups, series connections may be the best solution. 

Final Thoughts 

Understanding series battery connections is essential for anyone working with 12V power systems. 

• Series connections increase voltage and watt hours while keeping the capacity the same, making them ideal for 24V and 48V systems. 
• They provide better efficiency over long distances, making them useful for large off-grid solar setups, inverters, and industrial applications. 
• When setting up a series connection, always use identical batteries, match the charger voltage, and ensure proper wiring to avoid imbalances and inefficiency. 

If your system requires a higher voltage setup, a series connection may be the way to go. For most 12V off-grid applications, parallel connections are more practical. Knowing the difference between the two will help you choose the right setup for your needs.