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Calcimator

Battery Bank Sizing Calculator

Size a battery bank: calculate series/parallel configuration, total batteries, and usable capacity for off-grid and backup systems.

Inputs

kWh/day
days
V
%

IEEE 1115/1561: flooded lead-acid 50% DOD (long life); VRLA 50%; LiFePO4 80–90%; NiCd 100%

Ah
V

Results

Total Batteries

20 batteries

Usable Capacity

24 kWh

≈ 24 loads of laundry

Total Energy Required20 kWh
Batteries in Series4 per string
Parallel Strings5 strings
How to Use This Calculator
  1. Enter your Daily Load in kWh/day — sum all loads multiplied by their daily hours of use.
  2. Set the Days of Autonomy — the number of days the bank must supply power without recharging (typically 1–3 days for solar backup).
  3. Enter the Battery Voltage (individual cell/unit): common values are 2V, 6V, 12V, or 48V.
  4. Set the Depth of Discharge: lead-acid ≈ 50%, LiFePO4 ≈ 80–90%. Deeper discharge shortens battery life.
  5. Enter the Battery Capacity in Ah (20-hour rate) and your target System Voltage (12, 24, or 48 V DC bus).
  6. Review Batteries in Series, Parallel Strings, and Total Batteries, then verify Usable Capacity in kWh meets your autonomy requirement.

How the result changes with Battery Voltage

Battery VoltageTotal BatteriesUsable Capacity
6.640 batteries26.4 kWh
1815 batteries27 kWh
3210 batteries32 kWh
4310 batteries43 kWh

What each input means

Daily Load
Average daily energy consumption to be supplied by batteries.
Days of Autonomy
Number of days the battery bank should power loads without recharging.
Battery Voltage
Nominal voltage of each individual battery (e.g., 2V, 6V, 12V, 48V).
Depth of Discharge
Maximum depth of discharge per IEEE 1115 (flooded lead-acid) and IEEE 1561 (VRLA). Lead-acid flooded: max 80% per IEEE 1115 but 50% recommended for longevity; VRLA (AGM/Gel): 50% recommended; LiFePO4: 80–90% per manufacturer.
Battery Capacity
Amp-hour capacity of each individual battery at the 20-hour rate.
System Voltage
Target DC bus voltage of the battery system (e.g., 12, 24, 48V).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Daily Load = 10, Days of Autonomy = 2, Battery Voltage = 12, Depth of Discharge = 50 = 6 input(s) provided
  2. Calculate Total Batteries
    Total Batteries = max(totalBatteries
    20 = 20
  3. Calculate Usable Capacity
    Usable Capacity
    24 = 24
  4. Calculate Total Energy Required
    Total Energy Required
    20 = 20
  5. Calculate Batteries in Series
    Batteries in Series = max(batteriesInSeries
    4 = 4

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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