Understanding the difference between wiring batteries in series vs. parallel is critical if you have a multiple battery system. How you connect your batteries will determine how they perform in different applications. Let’s look closer at how to wire batteries in series vs. parallel and when each method is appropriate.
These two batteries are wired in seriesThe main difference in wiring batteries in series vs. parallel is the impact on the output voltage and the capacity of the battery system. Batteries wired in series will have their voltages added together. Batteries wired in parallel will have their capacities (measured in amp-hours) added together. However, the total available energy (measured in watt-hours) in both configurations is the same.
For example, wiring two 12-volt batteries with 100 Ah capacities in series will output 24 volts with a 100 Ah capacity. Wiring the same two batteries in parallel will output 12 volts with a 200 Ah capacity. Thus, both systems have a total available energy of 2400 watt-hours (watt-hours = volts x amp-hours).
Additionally, batteries wired in series and parallel configurations should all have the same voltage and capacity rating. Mixing and matching voltages and capacities can lead to problems that may damage your batteries.
To wire multiple batteries in series, connect the positive terminal of each battery to the negative terminal of the next. 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 series. Let’s look at two examples to make this clear.
The first example is two 100 Ah batteries 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 total system voltage is 24 volts, and the total capacity is 100 Ah.
The second example is wired the same way but with a third battery. The voltages of all three batteries add together, resulting in a system voltage of 36 volts, but the capacity remains at 100 Ah.
The power a device consumes is equal to 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). That same device operating at 24 volts would only draw 15 amps (24 x 15 = 360).
Wiring batteries in series provides a higher system voltage which results in a lower system current. Less current means you can use thinner wiring and will suffer less voltage drop in the system.
In addition to power draw, charging works the same way. Consider an MPPT solar charge controller rated at 50amps. a 50A x 12V controller could only handle 600 watts of solar, but at 24Vx50A it could handle 1200 watts!
In general, operating larger power systems can see big benefits in running batteries in series at higher voltages.
In a battery system wired in series, you cannot get lower voltages off the battery bank without using a converter. Either all equipment needs to function at the higher voltage or an additional converter is needed to use 12V appliances on the system.
To wire multiple batteries in parallel, you connect all of the positive terminals together and all of the negative terminals together. Since all of the positive and negative terminals are connected, you can measure the system output voltage across any two positive and negative battery terminals. Let’s look at two examples to make this clear.
The first example is two 100 Ah batteries wired in parallel. The positive terminal on the first battery is connected to the positive terminal on the second. Likewise, the negative terminals of both batteries are also connected. The total system voltage is 12 volts, and the total capacity is 200 Ah.
The second example is wired the same way but with a third battery. The capacities of all three batteries add together, resulting in a total capacity of 300 Ah at 12 volts.
The main advantage of wiring batteries in parallel is that you increase the available runtime of your system 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.
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 harder to operate and less efficient when operating at lower voltages.
The limit on how many batteries you can wire in series typically depends on the battery and manufacturer. For example, Battle Born allows up to four of their lithium batteries to be wired in series to create a 48-volt system. Always check with your battery manufacturer to ensure you do not exceed their recommended limit of batteries in series.
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. Keep in mind that the more batteries you have in parallel, the longer it will take to charge the system.
With very large parallel battery banks comes much higher current availability as well. This means the proper system fusing is critical to prevent accidental shorts that could have catastrophic consequences with so much current available.
You cannot wire the same batteries in series and parallel as you would short the system, but you can wire sets of batteries in series and parallel to create a larger battery bank at a higher voltage.
The photo below wires two batteries in series to get 24V then that set is wired in parallel to another set of 24V batteries. Think of each set of series batteries as one battery. You must “create” another set of batteries equal to the voltage of the first to wire them in parallel.
Here is another graphic of our heated lithium batteries wired in a series-parallel configuration. This setup would yield a 24V 200AH bank. While the amp hour is smaller, the power is the same because of the higher voltage.
Besides making sure you have the correct voltage charger, batteries in series vs. parallel charge the same way. For batteries wired in series, connect the positive charger cable to the positive terminal on the first battery in series and the negative charger cable to the negative terminal on the last battery in the series. For even charge across a parallel bank, connect your charge in the same fashion: positive connect to first battery, and negative connected to last battery.
Optionally, a multi-bank battery charger may provide faster charge times for series and parallel battery banks. As always, refer to the manufacturer’s recommendation for the best way to charge your batteries.
➡ Also be sure to read our article on Charging Lithium Batteries: The Basics.
Series connections provide a higher voltage which is slightly more efficient. This means that batteries wired in series can last marginally longer than batteries wired in parallel. However, batteries connected in series vs. parallel will provide roughly the same amount of runtime. Let’s take a look at a quick example that explains why this is true.
Two 12-volt batteries with a 100 Ah capacity are powering a 240-watt device. These two batteries wired in series will provide 24 volts and 100 Ah of capacity. The current draw of the device will be ten amps (24 x 10 = 240). The theoretical runtime of the series system is 100 Ah divided by ten amps, which is ten hours.
Conversely, the same two batteries in parallel provide 12-volts and 200 Ah of capacity. The device’s current draw in this setup is 20 amps (12 x 20 = 240). The theoretical runtime of the parallel system is 200 Ah divided by 20 amps, which is also ten hours.
Deciding between connecting your batteries in series vs. parallel is often dictated by the needs of the devices you’re powering. For general boat and RV applications wiring batteries in parallel provides the simplest wiring and common voltage, however, for large applications beyond 3000 watts of power, using higher voltage series connections might be best. Now that you understand how each wiring configuration works, you can determine the best option for your needs and proceed with confidence.
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