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Engineering

Battery Backup Calculator

Use this battery backup calculator to calculate estimate battery runtime from capacity, voltage, load, efficiency, and depth of discharge.

battery backupruntimecapacityinverter

Calculator

Calculate instantly

Calculator Inputs

Choose what you want to calculate, enter realistic values, adjust units where shown, and use the scenario section for repeated-use planning.

Input and Formula Breakdown

This calculator applies the formula Runtime = Ah x V x DoD x efficiency / load. Enter each value with the matching unit, and AZCalculate updates the result instantly.

Battery capacity
200 Ah
Battery voltage
12 V
Depth of discharge
80 %
System efficiency
90 %
Load
500 W
Runtime
3.46 hours
Usable energy
1,728 Wh

Scenario and Comparison

Current

3.46 hours

Projected

41.47

Adjusted

3.8

Visual Comparison

Current result3.46
Projected usage41.47
Comparison scenario3.8

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Trust note

Planning estimate

Use this result as a practical estimate. Real-world conditions, local rules, measurement tolerance, and changing inputs can affect the final outcome.

Medium risk contextDifficulty: professionalConfidence estimate: 95/100Reviewed 2026-05-18Reviewed by: Engineering content reviewerCalculator vuces-2.1 / Formula vformula-1.03 sources listed

Formula and Explanation

Runtime = Ah x V x DoD x efficiency / load

This calculator applies the formula Runtime = Ah x V x DoD x efficiency / load. Enter each value with the matching unit, and AZCalculate updates the result instantly.

Variable descriptions

capacity(Ah)
Battery capacity: Battery capacity measured in Ah, entered as a known value.
voltage(V)
Battery voltage: Battery voltage measured in V, entered as a known value.
dod(%)
Depth of discharge: Depth of discharge measured in %, entered as a known value.
efficiency(%)
System efficiency: System efficiency measured in %, entered as a known value.
load(W)
Load: Load measured in W, entered as a known value.

Formula Notes

  • Use consistent units for values that are multiplied, divided, or compared.
  • Results may be rounded for readability, while the calculator keeps greater precision internally.
  • Real-world measurements and assumptions can introduce small differences from the calculated estimate.

Common uses

  • Plan backup power
  • Size batteries
  • Compare runtime scenarios

Assumptions

What this calculation assumes

  • Calculations assume compatible engineering units and idealized conditions.
  • Safety factors, tolerances, material variation, and standards should be reviewed separately.
  • Inputs are assumed to describe the same scenario and use compatible units.
  • Results may be rounded for readability.

Avoid mistakes

Quick checks before you rely on the result

  • Ignoring safety factors.
  • Using rated values instead of actual operating conditions.
  • Mixing units, periods, currencies, or measurement systems without converting first.
  • Rounding intermediate values too early.

Step-by-Step Explanation

Follow the reasoning, not only the final number.

  1. 1

    Set up the calculation

    Enter the known values in the calculator fields.

    Starting with clearly defined values and units prevents the most common calculation errors.

  2. 2

    Work through step 2

    Keep the units consistent with the labels shown beside each input.

    This step transforms the known values into the form required by the formula.

  3. 3

    Work through step 3

    Apply the formula: Runtime = Ah x V x DoD x efficiency / load.

    This step transforms the known values into the form required by the formula.

  4. 4

    Interpret the result

    Review the primary result and supporting values.

    Compare the result with your real-world goal, such as plan backup power.

Worked example

Practical battery backup calculator example

Known values

  • Battery capacity: 200 Ah
  • Battery voltage: 12 V
  • Depth of discharge: 80 %
  • System efficiency: 90 %
  • Load: 500 W

Calculation

  1. 1. Start with the known values shown for this battery backup calculator scenario.
  2. 2. Substitute those values into Runtime = Ah x V x DoD x efficiency / load.
  3. 3. Evaluate the expression and keep the requested unit and rounding.

Result and meaning

Runtime: 3.46 hours; Usable energy: 1,728 Wh

Calculator guide

About this Battery Backup Calculator

Estimate battery runtime from capacity, voltage, load, efficiency, and depth of discharge.

References

Sources used for this calculator

Found something that does not look right?

We work hard to keep every calculator accurate and useful. If you notice a calculation error, missing option, or unclear explanation, please let us know so we can review and correct it promptly.

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Calculator usage

Usage information loads after the calculator is ready.

FAQ

Battery Backup Calculator FAQs

How does the battery backup calculator work?+

It uses Runtime = Ah x V x DoD x efficiency / load and calculates the result from the values you enter.

Can I copy or print the result?+

Yes. AZCalculate calculator pages include copy, share, and print actions.

Should I include a safety factor?+

Yes for real engineering decisions. Use applicable standards and professional review.

Which unit system should I use?+

Use a consistent unit system and convert all inputs before combining them.

How should I use this calculator result?+

Use it as an estimate and compare it with the formula, assumptions, and examples shown on the page.

Why can real-world results differ?+

Real-world inputs can include local rules, changing rates, measurement tolerances, and conditions outside the core formula.

What information do I need for the battery backup calculator?+

Enter the known values requested by the calculator. Use the unit selectors where available and make sure the values describe the same scenario.

How accurate is the battery backup calculator?+

The calculator follows the formula shown on this page. Accuracy depends on the values, units, assumptions, and rounding used in your scenario.

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