12V Install Tools & Testers

Battery Bank Series & Parallel Calculator

Work out the voltage, capacity and energy of a bank of identical batteries, and how many you need.

Batteries in series add their voltage. Batteries in parallel add their capacity. Enter one battery and the system voltage you want, and this works out the layout, the bank's voltage, amp-hours and energy, and optionally how many strings you need for a target capacity. It assumes every battery in the bank is the same model. Everything is worked out in your browser. Nothing is saved or sent anywhere.

1. One battery

2. Your bank

Whole number. Ignored if you enter a capacity target below.
Get it from the Daily Energy Use & Battery Size Calculator.

3. Results

How it was worked out

    Before you connect batteries together

    • This works out the bank's nominal figures only. It is not a wiring design and doesn't check cables, fuses, isolators, chargers or the battery management system.
    • Follow your battery maker's rules. Limits on series and parallel connection differ between makers and models. For example, Victron's Lithium NG 12.8V manual allows up to four 12.8V batteries in series and says batteries in a series string must have the same capacity rating and part number. Some batteries may not allow series connection at all.
    • Fully charge and balance each battery before connecting them together. Victron's manuals and its Wiring Unlimited book both say to do this.
    • Fuse the bank as the battery maker specifies. For example, Victron's Lithium NG manual says to fuse each series string on the positive side, or each battery when they're in parallel. Fuse and cable sizing need a separate check. See our 12V Cable and Fuse Size Guide.
    • Wire parallel batteries so each one sees the same current path, for example with busbars or equal-length cables, as Victron's Wiring Unlimited book explains.
    • Lead-acid batteries in series drift apart over time. Victron recommends a battery balancer for series lead-acid banks, and its Wiring Unlimited book suggests a practical maximum of about three or four parallel strings.
    • Lithium batteries rely on their battery management system. Check that yours supports the layout you plan, and that your charger suits the bank's voltage and chemistry.
    • A battery bank can deliver very high fault current. Have your installation checked by a qualified auto electrician, and check the Australian requirements that apply to your vehicle or caravan. Any 240V work must be done by a licensed electrician.

    Sources

    Next steps

    Work out the capacity you need with the Daily Energy Use & Battery Size Calculator, see how long your bank will last with the Battery Runtime Calculator, and compare chemistries in Lithium vs AGM Battery for Camping.

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