Understanding Battery Capacity in Watt-Hours
Battery capacity is often labeled in amp-hours. Watt-hours give a clearer energy measurement. They include both battery voltage and charge capacity. Multiply voltage by amp-hours to obtain watt-hours. A 12 V, 100 Ah battery stores 1,200 Wh. This equals 1.2 kWh before practical losses.
Nominal Energy Versus Usable Energy
Nominal energy is the battery's theoretical stored energy. Real systems rarely use every rated watt-hour. Depth of discharge protects battery life and reliability. A reserve keeps energy available for unexpected demand. Aging can also reduce effective battery capacity. Cold conditions may further reduce available energy. This tool combines those factors into usable energy.
Series and Parallel Battery Banks
Series wiring increases total bank voltage. Amp-hour capacity stays unchanged in a series string. Parallel wiring increases the available amp-hour capacity. Voltage stays unchanged across parallel strings. Mixed banks can use both arrangements together. Matching batteries is important for safe bank operation. Always follow manufacturer wiring and protection guidance.
Efficiency and Runtime Estimates
Loads may receive less energy than batteries store. Inverters, converters, cables, and internal resistance create losses. The calculator applies efficiency percentages to usable energy. Runtime then divides delivered energy by total load power. Standby power can be included as continuous overhead. Peukert adjustment can estimate high-current lead-acid behavior. It is only an approximation for planning purposes.
Choosing the Right Capacity
Start with realistic load power and operating time. Add reserve capacity for uncertainty and future growth. Consider expected temperature and battery age. Compare batteries using watt-hours instead of amp-hours alone. Different voltages can make identical amp-hour ratings misleading. Energy density also matters in mobile applications. Careful estimates improve runtime planning and battery selection decisions.
How to Use This Calculator
Enter battery voltage and rated capacity first. Choose Ah or mAh for the capacity unit. Set series and parallel battery counts. Add usable-capacity limits and efficiency values. Enter a load in watts or amps. Press Calculate to update every result. Export the current calculation when documentation is needed.