Understanding the difference between wiring batteries in series vs. parallel is critical if you have multiple batteries you want to connect together in a larger bank. It's something that is done all the time, even inside batteries, so it's important to understand. How you connect your batteries will determine how they perform in different applications. Let's look at how to wire batteries in series vs. parallel and when each method is appropriate.
What's The Difference Between Wiring Batteries In Series Vs. Parallel?
The main difference between wiring batteries in series and parallel is the impact on the output voltage and current capacity of the battery system. Batteries wired in series will add their voltages while the current capacity stays the same. Conversely, batteries wired in parallel will have their current capacities added together while their voltage remains the same. However, the total available energy (measured in watt-hours) in both configurations is the same if using the same number of batteries. How you wire batteries does not give you more energy capacity.
For example, wiring two 12-volt batteries with 100 Ah capacities in series will output a 24-volt system with a 100 Ah capacity. This means that the batteries will be able to put out 100 amps at 24volts for a total available energy of 2400 watt-hours (watt-hours = volts x amp-hours)
Wiring the same two batteries in parallel will output a 12-volt system with a 200 Ah capacity. Thus, both systems have a total available energy of 2400 watt-hours (watt-hours = volts x amp-hours).
Before we go further its important to note that batteries wired in series and parallel should always be the same type and size battery. Mixing types and sizes can cause damage to batteries.
When referring to batteries wired together to make a larger set of batteries we refer to the connected batteries as a "bank" of batteries.
⚡️ How about wiring solar panels in series vs. parallel? Find out here.
How To Wire Batteries In Series
To wire multiple batteries in series, connect each battery's positive terminal to the next's negative terminal. Then, measure the system's total output voltage between the negative terminal of the first battery and the positive terminal of the last battery in the series.
For example, two 12-volt 100 Ah batteries are wired in series. As you can see, the positive terminal on the first battery is connected to the negative terminal on the second. Thus, the system's voltage will increase to 24 volts while the total capacity will remain at 100 Ah.
Similarly, with 3 - 12-volt 100Ah batteries wired in series, the voltages of all three batteries add together, resulting in a system voltage of 36 volts and a capacity of 100 Ah. You can basically think of it like making one higher-voltage battery.
Advantages of Batteries in Series
The power a device consumes equals its operating voltage multiplied by the current it draws. For example, a 360-watt device operating at 12 volts would draw 30 amps (12 x 30 = 360), while the same device operating at 24 volts would only draw 15 amps (24 x 15 = 360).
Wiring batteries in series provides a higher system voltage, resulting in a lower system current. Less current means you can use thinner wiring and suffer less voltage drop in the system.
Charging and power drawing work the same way. Consider an MPPT solar charge controller rated at 50amps. A 50A x 12V controller can only handle 600 watts of solar, but at 24Vx50A, it can handle 1200 watts!
In general, larger power systems can benefit from running batteries in series at higher voltages. In fact its the same reason our power grid operates at such high voltages, it carries more power at lower current with smaller wires.
Disadvantages
How Many Batteries Can You Wire In Series?
The limit on how many batteries you can wire in series typically depends on the battery and manufacturer. At Battle Born Batteries, the maximum is four batteries wired together in series, creating a 48-volt system. Always check with your battery manufacturer to ensure you do not exceed their recommended limit.
Wiring Batteries In Parallel
To wire multiple batteries in parallel, connect all of the positive terminals together and then all of the negative terminals together. Since all positive and negative terminals are connected, you can measure the system output voltage across any of the positive and negative battery terminals.
For example, two 12-volt 100 Ah batteries are wired in parallel. The positive terminal on the first battery connects to the positive terminal on the second. Likewise, the negative terminals of both batteries are also connected. The system has a voltage of 12 volts and a total capacity of 200 Ah.
The same principles apply when adding a third battery. The capacities of all three batteries add up to a total capacity of 300 Ah at 12 volts. (This pack could output 300 amps per the rating of the 100 amp batteries)
Advantages
The main advantage of wiring batteries in parallel is that you increase your system's available capacity while maintaining the voltage. Since the amp-hour capacities are additive, two batteries in parallel double your runtime, three batteries triple it, and so on.
Another advantage to wiring batteries in parallel is that if one of your batteries dies or has an issue, the remaining batteries in the system can still provide power, as they basically bypass it.
Disadvantages
The main drawback to wiring batteries in parallel vs. series is that the system voltage will be lower, resulting in a higher current draw. Higher current means thicker cables and more voltage drop. Larger power appliances and generation are less efficient when operating at lower voltages.
How Many Batteries Can You Wire In Parallel?
There is no limit to how many batteries you can wire in parallel. The more batteries you add in a parallel circuit, the more capacity and longer runtime you will have available. Remember that the more batteries you have in parallel, the longer it will take to charge the system.
Huge parallel battery banks also have much higher current availability. This means the proper system fusing is critical to prevent accidental shorts that could have catastrophic consequences with so much current available.
Can You Wire Batteries In Series and Parallel?
You cannot simultaneously wire individual batteries in series and parallel without shorting the system. However, you can wire batteries in series and connect the sets in parallel to form a larger battery bank with a higher voltage.
The photo below shows a portion of a very large battery bank. Four 12-volt 270 Ah GC3 Battle Born Batteries are wired together in series to increase the voltage. This creates a 48-volt 270Ah system. Think of each set of four batteries wired together as one battery. To wire them in parallel, you must "create" another set of batteries equal to the voltage of the first. The system below includes 16 sets of 48V "batteries" wired together for 48 volts and 4,320Ah. This equates to 207,360 watt hours of storage, which is a lot! This runs a whole lodge.
Charging Batteries In Series Vs. Parallel
Besides ensuring you have the correct voltage charger, batteries in series vs. parallel charge the same way.
Series
For batteries wired in series, connect the positive charger cable to the positive terminal on the first battery in the series and the negative charger cable to the negative terminal on the last battery in the series.
Parallel
For even charging across a parallel bank, connect your charge similarly: positive connection to the first battery and negative connection to the last battery.
Optionally, a multi-bank battery charger may provide faster charge times for series and parallel battery banks. These work by charging each batter.y individually instead of the set (or bank) as a whole. Refer to the manufacturer's recommendation for the best way to charge your batteries.
➡ Read our article on Charging Lithium Batteries: The Basics.
Batteries In Series Vs. Parallel: Which Is For You?
Choosing whether to connect your batteries in series or parallel depends on the specific needs of the devices you are powering. For general boat and RV applications, wiring batteries in parallel at 12V provides the most uncomplicated wiring and standard voltage. However, higher-voltage series connections might be best for large applications beyond 3000 watts. Now that you understand how each wiring configuration works, you can determine the best option for your needs and proceed confidently.
Frequently Asked Questions:
Is it better to put batteries in series or parallel?
There is no better way to wire batteries; it all depends on your voltage needs. High power needs benefit from higher voltages, while lower voltages to match the needs of a vehicle simplify systems.
Do Batteries Last Longer In Series Or Parallel?
Generally, there is no benefit to wiring batteries in series or parallel, and you will get the same runtime out of them. However, there is one caveat when running high-power appliances.
Series connections provide a higher voltage, which is slightly more efficient when using high-power inverters. This means that batteries wired in series can last marginally longer than batteries wired in parallel. However, overall performance remains the same, and batteries connected in series and parallel will provide the same amount of energy. Let's look at a quick example explaining why this is true.
Two 12-volt batteries with a 100 Ah capacity power a 240-watt device. These two batteries, wired in series, will provide 24 volts and 100 Ah capacity. The device's current draw will be ten amps (24 x 10 = 240). Thus, the theoretical runtime is ten hours: 100 Ah divided by 10 amps.
Conversely, the same two parallel batteries provide 12 volts and 200 Ah of capacity. The device's current draw in this setup is 20 amps (12 x 20 = 240). Thus, the theoretical runtime is also ten hours: 200 Ah divided by 20 amps.
However, 10 amps incurs less resistance than 20 and thus is slightly more efficient, reducing losses in wires and some electrical devices.
Is series or parallel battery wiring more powerful?
There is no difference in energy between parallel and series wiring when using the same number of batteries. You can also get the same power out of both series and parallel configurations. The series will just have higher voltage, and the parallel will have higher current.
However, higher voltages generally allow for higher power appliances and inverters, so series will allow for large appliance use.
Which is safer, wiring in series or parallel?
As long as you do not wire more than four 12V batteries in series (48 volts), there is not much difference between series and parallel in safety. Beyond 50 volts, series voltages can get dangerous to work with and require special precautions.
Does putting lithium batteries in series increase amperage?
No, series connections of any battery type do not increase amperage output. However, batteries can be wired in series (say 2 , 12V batteries) then another set of 2 in series can be connected in parallel to that set, doubling the amperage of the series set. See our series parallel paragraph in this article for more details.
