FreeTools Labs Glossary
Battery runtime
Understand how capacity, voltage, load and efficiency relate to runtime, and why a theoretical battery estimate can differ in use.
Relevant tool
Battery Runtime & Capacity Calculator
Calculate energy, runtime, charge time and S/P values.
Open Battery Runtime & Capacity Calculator →Battery runtime is governed by usable stored energy and the load that draws it; an Ah value becomes comparable to watt-hours only with voltage.
Functions and inputs
Six separate paths cover runtime, energy/capacity conversion, required capacity, charging time, series/parallel nominal packs, and a two-scenario comparison. Ah and mAh describe charge; Wh and kWh describe energy, so a voltage is required when moving between them.
Calculation model
The runtime estimate follows the energy path from nominal capacity through the entered usable-capacity and efficiency factors: Wh = Ah × V; Whusable = Whnominal × fcapacity × η; h = Whusable ÷ W.
How the calculator model works
Runtime uses either energy and power or capacity and current, with entered usable-capacity and efficiency factors. Charging time distinguishes the ideal result from the result adjusted by the entered charging efficiency; pack and comparison results are nominal values, not a quality ranking.
Checked examples
This checked battery scenario traces voltage, capacity, losses and continuous power draw in that order: 12 V × 10 Ah = 120 Wh; × 0.8 × 0.9 = 86.4 Wh; ÷ 20 W = 4.32 h → 4 h 19 min. S=3, P=4: 11.1 V, 12 Ah, 133.2 Wh.
Units, display and interpretation
Treat the displayed duration as a steady-load estimate; the presentation distinguishes minutes, hours and multi-day runtimes: Ah/mAh · Wh/kWh · V · A · W · h; <1 h → min, <48 h → h/min, ≥48 h → d/h.
Scope and limits
Loads, voltage and factors are constant entered values. Temperature, ageing, discharge curve, protection electronics and real charging behaviour are outside this mathematical model; it is not a pack-building instruction.