Battery Bank Size Calculator

Size an off-grid battery bank in amp-hours for the autonomy required.

About Battery Bank Size Calculator

Off-grid banks need several days of autonomy because consecutive cloudy days are common. Cold temperatures reduce available capacity, which is why an unheated battery room needs derating. Lead-acid banks are limited to about 50 per cent depth of discharge, so they must be roughly twice the size of a lithium bank for the same usable energy.

Formula

Battery Bank Size

Ah = daily draw × autonomy ÷ (depth of discharge × temperature derate)

autonomy: Days the bank must run without any charging
temperature derate: Capacity loss in cold conditions, significant for lead-acid

Worked example

With the default values below, Battery Bank Size Calculator returns Battery Bank Capacity of 694.4. Change any input above and every figure here is recalculated in your browser.

Inputs used

Daily energy consumptionminimum 0 kWh: 5 kWh
System voltageminimum 1 V: 48 V
Days of autonomyaccepts 0.5–14 days: 3 days
Depth of dischargeaccepts 0–100 %: 50 %
Derating for low temperatureaccepts 0–100 %: 10 %

Results

Battery Bank Capacity: 694.4 Ah
Battery Bank Capacity: 33.333 kWh
Usable Capacity: 347.2 Ah
Daily Draw: 104.17 Ah
Batteries in Series at 12 V Each: 4

Step by step

1Values used
2Battery Bank Size
3Battery Bank Capacity= 694.4 Ah
4Battery Bank Capacity= 33.333 kWh
5Usable Capacity= 347.2 Ah
6Daily Draw= 104.17 Ah
7Batteries in Series at 12 V Each= 4

Assumptions and limits

The result is derived only from the 5 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 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

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

Frequently Asked Questions

How is Battery Bank Size calculated?

Ah = daily draw × autonomy ÷ (depth of discharge × temperature derate) Off-grid banks need several days of autonomy because consecutive cloudy days are common. Cold temperatures reduce available capacity, which is why an unheated battery room needs derating.

Why does Battery Bank Size matter?

Lead-acid banks are limited to about 50 per cent depth of discharge, so they must be roughly twice the size of a lithium bank for the same usable energy.

What values do I need to enter?

This calculator takes 5 inputs: Daily energy consumption, System voltage, Days of autonomy, Depth of discharge, Derating for low temperature. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.