A Beginners Guide to Connecting Batteries in Series and Parallel

Disclaimer: Wiring batteries can be dangerous. Always wear eye and hand protection, and take off any metal jewelry around your hand (rings, bracelets, etc). If in doubt, hire a professional.

Want to learn the basics of writing batteries in series vs parallel?

In this article, I will explore the differences between series and parallel. I’ll also go a little deeper into each configuration to discuss why you might choose one over the other or a combination of both.

Wiring Batteries in Series vs Parallel

The voltage of batteries wired in series will be accumulated together to make one larger system voltage, and the capacity will only be that of single battery. For example, two 12V batteries in series will have a voltage of 24V. Batteries wired parallel will have the the total voltage of a single battery, and the capacity with increase  of the batteries cumulative total. 

When we are talking about wiring batteries in series and parallel into what’s known as a “battery bank”, it’s really a discussion of two tradeoffs: output voltage and capacity.

By changing the battery configuration, we can optimize our electrical circuit to provide what we need, while ensuring that the system is efficient enough to complete the tasks required.

What is Battery Capacity?

Battery capacity is related to how much energy can be extracted from your battery in a certain timeframe. The most common measurement is Amp Hours (Amp-hr). For example, a battery with a rating of 10Ar can provide a maximum of 10 Amps in a circuit over the course of an hour. It's important to note that the current is not capped out at 10 Amps. That same battery can also provide 20 Amps for 30 minutes before running out of juice. 

Watt-hours can also be used as a measurement for battery capacity. The formula for watt-hours is:

(voltage * current) x (total number of hours) = watt-hours

How to Connect a Battery in Series?

To connect batteries in a series, use a wire to connect the negative terminal of the first battery to the positive terminal of the second battery. Use another set of cables to connect the open positive and negative terminals to connect to the circuit. Always use wire of the same gauge and length when connecting batteries. 

Should I Connect Battieries with Differnet Voltages in Series?

No, It’s always best to wire identical batteries in series. Avoid any situation where one battery is doing more work than another. Always use identical batteries in series and parallel.

In theory, you could connect batteries with different voltages in series as long as they have the same capacity rating.

But there are other factors such as temperature that affect battery performance, so just don’t do it!

How to Connect Batteries in Parallel?

Wiring batteries in parallel will result in a larger capacity. The output voltage will be that of one battery. In a series battery, 100% of the current is flowing through each battery, while in a parallel circuit, the current is split between each battery. and can power our system for longer.

To connect batteries in parallel, wire the positive and negative terminals together, and have lead in wire connected to the positive terminal of one battery, and another wire connected to the negative terminal of the other battery. Always use wire of the same gauge and length when connecting batteries.

Should I connect batteries in different voltages in Parallel?

No, always best to wire identical batteries with identical voltages and capacity in parallel and series. 

If you do wire two batteries together in parallel, the battery with the larger voltage will be distributed to the battery with a lower voltage.

Similar to how a dam overflows if it gets too much water. The smaller battery will be exposed to too much current, overheat, and possibly cause fire or explode. We never want one battery doing more work than the other.

In the real world, you will always have some kind of overcurrent protection devices like fuses and circuit breakers, so this scenario can be avoided if these measures have taken place. But in general, avoid mixing and matching batteries sizes wherever possible.

Here’s a great discussion in the stack overflow physicist group that goes deeper into this topic.

Can you wire in both Series and Parallel at the same time?

Yes. Wiring in series and parallel at the same time will increase the voltage of the system, while also increasing the capacity. You will need a minimum of 4 batteries to wire in series-parallel. 

Want the best of both worlds – more power and more capacity? Here’s a quick guide for wiring in series-parallel:

Key Takeaways

Key takeaways for wiring batteries in series and parallel:

  • Wiring batteries in series will increase voltage, and will not increase capacity.
  • Wiriing batteries in parallel will not increase voltage, but will increase capacity.
  • Wiring in series parallel will increase voltage and capacity.
  • Always use identical batteries with wiring them together.
  • Alwasy ask a professional if you are unsure.

I hope you learned a thing or two today, if you like this article, check out: Part 1: Resistance in Parallel, and Part 2: Current in Parallel.

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Written By Tim M

I’m on a journey to learn all I can about electronics - and I’m sharing everything. If you like my content, check out my Honda CX500 Restoration Project

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