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Battery Bank Sizing Calculator

Work out battery bank sizing instantly with clear inputs, formula shown and shareable results.

About Battery Bank Sizing Calculator

Bank energy is daily demand times days of autonomy divided by the permitted depth of discharge; dividing by system voltage converts it to amp-hours. Raising the system voltage cuts the amp-hour figure and therefore the cable size, which is why larger installations use 48 V rather than 12 V.

Formula

Battery bank

Wh = daily demand x autonomy days / DoD; Ah = Wh / system voltage

Worked example

With the default values below, Battery Bank Sizing Calculator returns Bank capacity required of 125.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Daily energy demand
2,400 Wh
Days of autonomy
2 days
System voltage
48 V
Depth of discharge
80 %

Results

Bank capacity required
125.00 Ah
Bank energy required
6,000 Wh
100 Ah blocks needed
2 blocks
Cells in series (3.2 V LFP)
15 cells

Step by step

  1. 1Values used
  2. 2Battery bank
  3. 3Bank capacity required= 125.00 Ah
  4. 4Bank energy required= 6,000 Wh
  5. 5100 Ah blocks needed= 2 blocks
  6. 6Cells in series (3.2 V LFP)= 15 cells

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 days of autonomy do I need?

Two to three days for off-grid solar in temperate climates, more where cloudy spells are long, less if a generator or grid backup exists.

Why prefer 48 V over 12 V?

The same power needs a quarter of the current, so cables and losses shrink by a factor of sixteen in I squared R terms.

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