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Battery Size from Load and Runtime — result sheet
Estimate the battery energy and amp-hour capacity needed for a load, runtime, voltage, usable-depth limit, efficiency, and reserve.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Load energy = P·t; required nominal energy = load energy ÷ (usable fraction × efficiency) × (1 + reserve); amp-hours = watt-hours ÷ voltage.
Battery sizing starts with the energy the load needs, then accounts for the fraction of the nameplate capacity that can be used, conversion losses, and a visible planning reserve. The result is an estimate of nominal watt-hours and amp-hours, not a promise of field runtime.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Load power — W; minimum 1.0E-6; maximum 1000000000
- Required runtime — h; minimum 1.0E-6; maximum 1000000
- Battery system voltage — V; minimum 1.0E-6; maximum 1000000
- Usable capacity fraction — %; minimum 1.0E-6; maximum 100
- Conversion efficiency — %; minimum 1.0E-6; maximum 100
- Planning reserve — %; minimum 0; maximum 1000
Worked example
| Input | Value |
|---|---|
| Load power | 100 |
| Required runtime | 8 |
| Battery system voltage | 12 |
| Usable capacity fraction | 80 |
| Conversion efficiency | 90 |
| Planning reserve | 10 |
An 800 Wh load requirement becomes about 1,222.22 Wh or 101.85 Ah at 12 V after the stated limits and 10% reserve.
Assumptions and limits
- Load power is constant for the stated runtime and the battery voltage is treated as a nominal operating voltage.
- Usable capacity and efficiency are entered as fractions of nameplate performance; actual capacity changes with discharge rate, temperature, age, chemistry, and cutoff voltage.
- The reserve is a planning multiplier only and does not replace manufacturer limits, protection settings, thermal design, or a battery-system safety review.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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