Battery Capacity Calculator (Ah / Wh)
Calculate the required battery capacity in Amp-hours (Ah) and Watt-hours (Wh) for a specified load and runtime.
AC loads lose energy in the inverter. 90% is typical; use 100% for direct DC loads.
Required Battery Bank Capacity
@ 12V Nominal (1.39 kWh nominal bank)
Step-by-Step Engineering Calculation
- 1Total Energy Consumed:
- 2Total Battery Bank Energy (accounting for 80% DoD & 90% Eff):
- 3Required Capacity:
Formula & Theory
Computes total nominal battery bank capacity required to sustain target runtimes without over-discharging.
Variable Definitions
- P_load:
- Load Power (Watts (W)) – Operating power draw
- T:
- Desired Runtime (Hours (h)) – Target runtime between charges
- Ah:
- Required Capacity (Amp-hours (Ah)) – Calculated nominal capacity
Worked Engineering Example
Off-Grid Security Camera System
A 40W camera and router running for 24 hours on a 12V battery system with 80% DoD and 90% efficiency.
- Load: 40 W
- Runtime: 24 hours
- Voltage: 12 V
- DoD: 80%
- Efficiency: 90%
Key Assumptions
- •Constant average power draw.
Limitations & Safety Scope
- •Temperature derating during cold weather requires sizing adjustments for outdoor installations.
Frequently Asked Questions
How do I convert Wh to Ah?
Divide Watt-hours by nominal system voltage: Ah = Wh / Volts.
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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.