PowerCalcLab

Battery calculator

Battery Series / Parallel Calculator

Series connections add voltage. Parallel connections add amp-hour capacity. Enter one battery's rating and the layout to see the complete bank without mixing those rules up.

Results update as you type. The calculator runs entirely in your browser — nothing you enter is sent anywhere.

Combined battery bank51.2 V · 200 Ah

Calculation breakdown

Stored energy10.24 kWh
Connection4 in each series string, 2 strings in parallel4S2P
Total batteries8
Voltage = unit voltage × series; Capacity = unit Ah × parallel
= 12.8 V × 4; 100 Ah × 2
= 51.2 V; 200 Ah; 10.24 kWh
  • Only identical batteries of the same type, capacity, age and state of charge should be combined into one bank.

Before you rely on this

Large battery banks can deliver destructive fault current. Use manufacturer-approved topology, balanced cabling, correctly rated fuses and disconnects, and qualified installation review where required.

Method

How the number is reached

In series, the positive terminal of one battery connects to the negative of the next: voltages add while amp-hour capacity stays unchanged. Parallel strings share positive and negative buses: amp-hours add while voltage stays unchanged.

Energy is conserved across the arrangement. The energy of one battery multiplied by the total battery count equals bank voltage multiplied by bank amp-hours.

V_bank = V_unit × series count
Ah_bank = Ah_unit × parallel strings
Wh_bank = V_bank × Ah_bank
Battery count = series × parallel

Symbols

S
Batteries in series per string
P
Number of parallel strings

Worked examples

The same maths, applied

Example

Eight 12.8 V 100 Ah batteries in a 4S2P bank

Four batteries form each string and two identical strings are paralleled.

Voltage = 12.8 V × 4 = 51.2 V
Capacity = 100 Ah × 2 = 200 Ah
Energy = 51.2 V × 200 Ah = 10.24 kWh

Result: 51.2 V · 200 Ah, using eight batteries.

Limits of the model

What it assumes, and where it stops

Assumptions

Every battery is identical and equally charged.

Series strings use the same number of batteries and balanced cabling.

Not covered

The calculator does not verify manufacturer series/parallel limits, BMS compatibility, fuse sizes or conductor ampacity.

Parallel current sharing can be poor when interconnect resistance is unequal.

Sources

Where these figures come from

  • Wiring Unlimited — Battery bank wiringVictron EnergyManufacturer guidance for series, parallel and series/parallel battery banks, balanced current paths and connection safety.
  • SI UnitsNIST Office of Weights and MeasuresDefinitions of the volt, ampere, watt and joule used for the unit conventions on this site.

Next steps

Related calculators

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    Turn daily energy use into the nominal kWh and amp-hours your bank needs. The model accounts for days without charging, conversion loss, battery health, usable depth of discharge and whole-battery rounding.

  • Battery Usable Capacity Calculator

    The label capacity is not the energy available to your load. Set the starting and minimum state of charge, battery health and conversion efficiency to expose the usable window.

  • Ah to Wh Calculator

    Amp-hours describe charge, not energy. Multiply by the pack's nominal voltage to get watt-hours, the figure you need for runtime, shipping limits and solar sizing.

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Last meaningful update: 2026-08-19. This date changes only when the model, the sources or the guidance change.