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Battery Runtime Calculator

Estimate battery runtime in hours and minutes from voltage, capacity (Ah), load power (W), depth of discharge, and inverter efficiency.

1. Enter your numbers  →  2. Check the answer  →  3. Read the steps before you trust it

Ah
W
%

Typically 88-92% for pure sine inverters

Estimated Battery Runtime

Estimated Usable Runtime
5.76 hrs (5h 46m)

Continuous run duration until recommended cutoff voltage

Usable Stored Energy
864 Wh (0.86 kWh)
Total Nominal Capacity
1,200 Wh
Average Discharge Current
13.8889 A (0.14C)

Step-by-Step Engineering Calculation

  1. 1Total Nominal Energy: Enominal=12 V×100 Ah=1200.0 WhE_{\text{nominal}} = 12\text{ V} \times 100\text{ Ah} = 1200.0\text{ Wh}
  2. 2Usable Energy: Eusable=1200.0 Wh×80% DoD×90% Eff=864.0 WhE_{\text{usable}} = 1200.0\text{ Wh} \times 80\%\text{ DoD} \times 90\%\text{ Eff} = 864.0\text{ Wh}
  3. 3Estimated Runtime: T=864.0 Wh150 W=5.76 hoursT = \frac{864.0\text{ Wh}}{150\text{ W}} = \mathbf{5.76\text{ hours}} (5h 46m)
  4. 4Estimated Battery Current Draw: I=150 W12 V×0.9=13.89 AI = \frac{150\text{ W}}{12\text{ V} \times 0.9} = \mathbf{13.89\text{ A}} (Discharge Rate: 0.14C)

Formula & Theory

Runtime (hours) = (V_nom × Ah × DoD × η) / Load (Watts)

Calculates the operating duration of a DC battery bank or inverter system delivering continuous power to an electrical load.

Variable Definitions
Ah:
Battery Capacity (Amp-hours (Ah)) – Total nominal capacity rating of the battery
V:
Voltage (Volts (V)) – Nominal battery bank voltage (e.g. 12V, 24V, 48V)
DoD:
Depth of Discharge (Percentage (%)) – Usable capacity before recharging (50% Lead-Acid, 80-90% Lithium)
η:
Efficiency (Percentage (%)) – Conversion efficiency of inverter/regulator (typically 85-95%)

Worked Engineering Example

12V 100Ah LiFePO4 Inverter Setup

A 12V 100Ah Lithium battery powering a 150W television and mini fridge with 85% DoD and 90% inverter efficiency.

Inputs:
  • Voltage: 12 V
  • Capacity: 100 Ah
  • Load: 150 W
  • DoD: 85%
  • Efficiency: 90%
Result: Runtime = 6.12 hours (6h 7m), Usable Energy = 918 Wh

Key Assumptions

  • •Continuous constant power load throughout discharge.

Limitations & Safety Scope

  • •Lead-acid batteries experience capacity reduction at high discharge rates due to Peukert's law.

Frequently Asked Questions

Why should I not discharge lead-acid batteries below 50%?

Discharging flooded or AGM lead-acid batteries beyond 50% DoD causes severe plate sulfation, rapidly degrading battery lifespan and cycle count.

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How to Size a Battery Bank

Educational & Reference Notice: This calculator provides technical estimates based on standard physical formulas. Actual electrical installation, protective device sizing, and conductor selection must be verified against the applicable electrical code (NEC, IEC, CEC) by a licensed electrician or qualified professional engineer.