What&039s The Difference Between Wiring Batteries in Series Vs. Parallel?
Understanding the difference between wiring batteries in series and in parallel is critical if you have a multi-battery system. how you connect your batteries will determine their performance in different applications. Let’s take a closer look at how to connect batteries in series or 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 in parallel is the impact on the output voltage and capacity of the battery system. batteries connected in series will have their voltages added together. batteries connected in parallel will have their capacities (measured in amp-hours) added together. however, the total available power (measured in watt-hours) in both configurations is the same.
for example, connecting two 12 volt batteries with 100 ah capacities in series will produce 24 volts with a 100 ah capacity. Wiring the same two batteries in parallel will produce 12 volts with a capacity of 200 Ah. therefore, both systems have a total available power of 2400 watt-hours (watt-hours = volts x amp-hours).
Also, batteries connected in series and parallel must all have the same voltage and capacity rating. mixing and matching voltages and capacities can lead to problems that can damage your batteries.
series wiring batteries
To wire multiple batteries in series, connect the positive terminal of each battery to the negative terminal of the next. then measure the total system 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 clarify this.
The first example is two 100 Ah batteries connected in series. As you can see, the positive terminal of the first battery is connected to the negative terminal of the second. therefore, 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 the three batteries are added together, resulting in a system voltage of 36 volts, but the capacity remains at 100 ah.
advantages
The power a device draws is equal to its operating voltage multiplied by the current it draws. for example, a 360 watt device running at 12 volts would draw 30 amps (12 x 30 = 360). that same device running at 24 volts would only draw 15 amps (24 x 15 = 360).
connecting batteries in series provides a higher system voltage, which results in a lower system current. less current means you can use thinner wiring and you will experience less voltage drops in the system.
Apart from power consumption, charging works the same way. Consider a 50 amp mppt solar charge controller. a 50a x 12v controller could only handle 600 watts of solar, but at 24vx50a it could handle 1200 watts!
In general, running larger power systems can bring great benefits to running batteries in series at higher voltages.
disadvantages
In a series connected battery system, you cannot get lower voltages from the battery bank without using a converter. either all equipment must be run on the higher voltage or an additional converter is needed to use 12v appliances in the system.
parallel wiring batteries
To wire multiple batteries in parallel, connect all positive terminals together and all negative terminals together. Since all the positive and negative terminals are connected, you can measure the system output voltage at either of the positive and negative terminals of the battery. Let’s look at two examples to clarify this.
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 the three batteries are added, resulting in a total capacity of 300 ah at 12 volts.
advantages
The main advantage of connecting batteries in parallel is that it increases the available runtime of your system while maintaining voltage. Since amp-hour capacities are additive, two batteries in parallel double the runtime, three batteries triple it, and so on.
Another advantage of connecting batteries in parallel is that if one of your batteries dies or has a problem, the remaining batteries in the system can still provide power.
disadvantages
The main disadvantage of connecting batteries in parallel instead of series is that the system voltage will be lower, resulting in higher current draw. higher current means thicker wires and more voltage drop. larger appliances and power generation are more difficult to operate and less efficient when running at lower voltages.
how many batteries can you connect in series?
The limit on how many batteries you can connect in series generally depends on the battery and the manufacturer. For example, Battle Born allows up to four of its lithium batteries to be connected in series to create a 48-volt system. Always check with the battery manufacturer to make sure you don’t exceed the recommended number of batteries in series.
how many batteries can you connect in parallel?
There is no limit to the number of batteries you can connect in parallel. the more batteries you add in a parallel circuit, the more capacity and more runtime you have available. Keep in mind that the more batteries you have in parallel, the longer it will take for the system to charge.
with very large parallel battery banks you also get much higher current availability. This means that the proper fusing system is essential to prevent accidental short circuits that could have catastrophic consequences with so much current available.
can you connect the batteries in series and in parallel?
You can’t wire the same batteries in series and parallel, as that would short the system, but you can connect sets of batteries in series and parallel to create a larger battery bank with higher voltage.
The photo below connects two batteries in series to get 24v and then that set is connected in parallel to another set of 24v batteries. think of each set of batteries in series as a single battery. you must “create” another set of batteries equal to the voltage of the first to connect 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.
battery charging in series or parallel
Besides making sure you have the correct voltage charger, batteries in series vs. parallel are charged the same way. For batteries connected in series, connect the positive lead from the charger to the positive terminal of the first battery in series and the negative lead from the charger to the negative terminal of the last battery in series. For an even load on a parallel bank, connect your load the same way: positive connection to the first battery and negative connection to the last battery.
Optionally, a multi-bank battery charger can provide faster charge times for series and parallel battery banks. As always, check 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.
faq: do batteries last longer in series or in parallel?
series connections provide a higher voltage that is slightly more efficient. this means that batteries connected in series can last a little longer than batteries connected in parallel. however, batteries connected in series or parallel will provide approximately the same amount of run time. let’s take a look at a quick example that explains why this is true.
Two 12-volt batteries with a capacity of 100 Ah power a 240-watt device. these two batteries connected 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 run time for the series system is 100 Ah divided by ten amps, which is ten hours.
in contrast, the same two batteries in parallel provide 12 volts and 200 ah of capacity. the current draw of the device in this configuration is 20 amps (12 x 20 = 240). the theoretical running time of the parallel system is 200 ah divided by 20 amps, which is also ten hours.
batteries in series vs. parallel: which one is for you?
Deciding between connecting batteries in series or parallel often depends on the needs of the devices it powers. For general boat and RV applications, parallel battery wiring provides the simplest wiring and common voltage; however, for large applications over 3000 watts of power, it may be better to use higher voltage series connections. Now that you understand how each wiring configuration works, you can determine the best option for your needs and proceed with confidence.
