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Battery Bank Size Calculator

Size a battery bank in kWh and Ah and get the series/parallel wiring layout and unit count.

Inputs

Load and battery assumptions

Energy the bank must supply per day at the load side.

Days the bank must carry the load with no charging source. 1 day for a backup bank, 2-3 for off-grid.

Share of nameplate you cycle. Lead-acid 0.5, lithium 0.8-0.9. Staying inside the warranty value protects cycle life.

DC-to-AC and recharge losses. 0.9 typical; older inverters and lead-acid charging run lower.

Bank voltage: 12, 24, or 48 V for most DC systems; 51.2 V for a 16-cell lithium string.

Nameplate voltage of one unit: 12 V flooded/AGM, 12.8 V LiFePO4, 2 V cell for large banks.

Capacity of one unit at its own voltage, from the datasheet.

Result

Batteries to install
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Nameplate bank energy
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Strings in parallel
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Batteries in series per string
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Bank amp-hours required
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Usable energy at chosen DoD
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Installed bank amp-hours
—
Installed string voltage
—

What to check

  • Daily energy and autonomy days from metered data, not nameplate guesses.
  • Depth of discharge and cycle life from the battery datasheet; lead-acid and lithium differ sharply.
  • Whether the published amp-hour rating is at the 20-hour rate (most lead-acid) or a 1C rate.
  • Series count: battery voltage must divide the system voltage, or the string voltage will not match the inverter.
  • Cable ampacity and fuse size for the bank output; DC faults carry far more current than AC.
  • Ventilation, temperature range, and enclosure requirements for the chosen chemistry.

Related calculators

Planning estimate only. It does not select a chemistry, size DC overcurrent protection, or verify connector and cable ratings. Verify amp-hour ratings at the manufacturer stated discharge rate, and follow the locally adopted National Electrical Code (Article 706 for energy storage systems) plus the inverter manual.

Saved calculations

Keep the assumptions with the result.

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