Connecting a Battery Bank ~ Basics of Series vs Parallel

admin on April 3, 2013 · 28 comments

Difference Between Connecting a Battery Bank in Series vs a Parallel Series Configuration.

A Battery Bank connects a group of batteries together, either in a series or parallel. By connecting Batteries together, you can increase the voltage, amps or both. Amp hours refers to a steady current of one Ampere for one hour. Go here for more explanation

For Example: A 20 amp battery can discharge 10 amps for 2 hours or 5 amps for 4 hours. Amp hours represents the flow of electricity. Voltage represents the pressure of electricity.

Series Battery Bank

In a Series Battery Bank, a connection of a negative terminal of one battery to the positive terminal of the other battery is required.

For Example: If you have two 12V batteries, both at 10 amps, in a series connection, you will end up with 24V @ 10 amps. In a series array, voltage is added together but the amps stay the same. Then you are able to connect the open terminals to your Charge Controller if living off the grid or the Inverter if grid-tied.Connecting a Battery Bank

In a series battery bank configuration, it adds the voltage of the batteries but keeps the same amperage rating, also known as amp hours.

Parallel Battery Bank

In a parallel battery bank configuration it increases the amps but the volts stay the same. If you have two 12V batteries @ 10 amps each, your power will then be 12V at 20amps. You will require heavier cable wire however.

Parallel connects a positive terminal of one battery to the positive of another. Then connect the negative to negative terminals. To connect the power, attach a cable to one of the open terminals.

Series-Parallel Battery Bank

The third option is a Series-Parallel connection. Here the battery bank increases the Amps & Volts. You will require at least 4 batteries for this type of system.

If you have 2 sets of batteries already connected in parallel, you can then join them together to create a series. By doing so, you will have a bank that produces 12 volts at 20 amp hours.

Note: Never cross the open ended positive terminals together or it will short circuit the batteries and cause damage.

It is very important that the batteries that you are connecting have the same voltage and capacity rating. Meaning connecting a 12v battery to a 12v battery…NOT a 12v battery to a 6v battery….Otherwise you may end up with charging issues and premature battery life.

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28 Responses to “Connecting a Battery Bank ~ Basics of Series vs Parallel”

  1. Eric Coates says:

    This is a great tutorial. Our cottage has a large Series/Parallel system for running a refrigerator and some lights. Four banks of four 12 volt batteries, wired exactly as shown in your Series/Parallel diagram. But…the housing cabinet for them is breaking down and I want to move the batteries to a new cabinet. Unfortunately, the contractor who installed the system has left the business. I can do this myself, but I am very nervous about making a mistake in the order of things. When connecting the final cables to the open negative and positive posts, which do I do first? Does it matter? May I send you a video of our system for comment/advice?

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  11. TheAudiophile13 says:

    Help please! I´m planning to install a second battery in the trunk for increased amp/hours. I´ll run the 0 gauge cables in parallel from the batt under the hood all the way to the trunk. Will I need fuses or isolators? Or should I just run the wires as shown in the vid with nothing in between?

  12. BatteryStuff says:

    A battery isolator is a good idea if the batteries are independent from one another in terms of use, but they can be recharged by the one alternator. If you are simply increasing your capacity (and CCA will go up as well), there is no need for additional accessories. The wires will do the job. But for safety reasons, secure the wires so they will safe. If one were disconnected, your system is down to one battery again.

  13. HOLLOWMASK99 says:

    this is an amazing tutorial

  14. KyleCarrington says:

    I wonder about this and I always thought the same, but recently, I was told if you are to parallel a bunch of 12V batteries together, because of the slightly different values of internal resistance – that if left uncharged (as in daily) – they will always be charging and discharging, fighting each other, until one dies a premature death, and that isolation is necessary – so is daily charging a must, then?

  15. flare745 says:

    The multiple battery bank diagram is confusing to me. It shows pairs of 6 volt batteries hooked together in parallel which leaves that pair at 6 volts but doubles the amps. then all eight pairs are connected in series which to me doubles the voltage each time for a total of 48 volts.

    It seems to me that what is needed is to hook each 6 volt pair in series making one 12 volt unit with the same amps then hooking these pairs together in parallel doubling the amps each time.

  16. BatteryStuff says:

    The diagram is for illustrative purposes only. The point is that if done correctly, there is no limit to how large your bank can be. The diagram does not show the total specs, but you’re right it is 48 volts with only double the capacity of a single battery. All sixteen batteries can be wired in different ways. Your method of keeping 12 volts will work as well.

  17. MrBodySMASH says:

    Thanks mate, that made things much easier for me to understand… more please

  18. rmnbrw says:

    This is true, recharging parallel connected battaries is not trivial. You should use either devices to enforce one directional current flow(special diode setup) or automatic circuit breaker.

  19. Jay Guy says:

    If you run two in a parallel wouldn’t it be more efficient to use the positive from one battery and the negative from the other. This way the second battery is not simply charging the one hooked up battery.

  20. Jay Guy says:

    Or if it is a starter battery you can run a isolater circute instead so when one charges full the second battery starts charging

  21. BatteryStuff says:

    Having a positive terminal connect to a negative terminal is a series connection, not parallel. But if you’re referring to an already existing parallel bank and you want to charge it from an external charger, yes you may connect to either one battery completely or both (with one terminal each).

  22. BatteryStuff says:

    If there is an unevenness of discharge between batteries, electricity will attempt to equalize and this will cause the battery with more capacity to feed into the batteries with less capacity.

    However, batteries in a bank will default to charging as equally as possible from an external source. So if there is an uneven discharge level between batteries, one will be overcharged and the other will be undercharged as a result.

  23. Jay Guy says:

    exactly what i was trying to the battery hooked up will discharge first but if you use power from both sides of the bank then it is like one big battery and they will drain even, now charging is another story, i don’t know if it draws more alternator amps this way

  24. Jay Guy says:

    series doubles the voltage and paralellel doubles the amps, now two 6 volt batterys isnt always going to have more amp hours and reserve compacity as long as the voltage is right and amperage ratings are right is what matters

  25. Jay Guy says:

    yep golf carts are good example of this many just use multpile 12 volt car batterys 3-6 depending on the model

  26. BatteryStuff says:

    Yes, in parallel banks it’s a good idea to hook your load/charging connections across the entire bank, not just the first battery. This will ensure the current will flow evenly from end to end.

  27. yzerman1997 says:

    Great simple video! I’ll be sure to share this link when I come across someone asking about battery wiring (I’m researching my approaching DIY solar project). Thanks!

  28. BatteryStuff says:

    You’re welcome. I’m glad to hear that the tutorial was very helpful to you.

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