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Parallel Battery Capacity Calculator

Work out parallel battery capacity instantly with clear inputs, formula shown and shareable results.

About Parallel Battery Capacity Calculator

Parallel strings add capacity and current capability while the voltage stays the same. The practical limit is circulating current: strings must be matched in age, chemistry and cable length, or the healthier strings will charge the weaker ones and waste energy as heat.

Formula

Parallel bank

Ah total = strings x Ah per string; voltage unchanged; max current = strings x per-string limit

Worked example

With the default values below, Parallel Battery Capacity Calculator returns Total capacity of 400.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Parallel strings
4 strings
Capacity per string
100 Ah
String voltage
12 V
Maximum discharge per string
50 A

Results

Total capacity
400.00 Ah
Total energy
4,800 Wh
Maximum discharge current
200.00 A
Bank voltage
12.00 V

Step by step

  1. 1Values used
  2. 2Parallel bank
  3. 3Total capacity= 400.00 Ah
  4. 4Total energy= 4,800 Wh
  5. 5Maximum discharge current= 200.00 A
  6. 6Bank voltage= 12.00 V

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

How many strings can I parallel?

Manufacturers usually recommend no more than three or four for lead-acid. Lithium packs with a shared BMS can go further if the interconnects are symmetric.

Why must cable lengths be equal?

Unequal resistance makes the strings share current unevenly, so one ages faster and the imbalance grows.

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