Enter your Load, System Voltage, and Runtime Duration into the Lead-Acid Battery Calculator, and it will figure out the Required Battery Capacity you need — plus your Load Current, Usable Capacity, and Efficiency Factor, all adjusted for your chosen Battery Type and Minimum Remaining Charge.
Required Battery Capacity
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Load Current
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Usable Capacity
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Efficiency Factor
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Battery current (in amps) is calculated by dividing the power consumption (in watts) by the system voltage. For example, a 100W load on a 12V system draws 8.33 amps (100W ÷ 12V = 8.33A).
Battery size is determined by multiplying the load current by the runtime duration, then dividing by the usable capacity percentage. Environmental factors and battery age may require additional capacity.
Lead-acid batteries should not be discharged below 50% of their capacity for optimal longevity. Deep discharges significantly reduce battery life and performance.
Temperatures below 0°F or above 85°F reduce battery efficiency by approximately 20%. Cold temperatures slow chemical reactions, while high temperatures can damage the battery and reduce capacity.
Batteries lose capacity over time due to sulfation and plate degradation. A battery older than 6 months may have reduced capacity, requiring oversizing to maintain reliable performance.
AGM (Absorbed Glass Mat) batteries are sealed and maintenance-free with good discharge rates. Gel batteries are also sealed but have slower discharge rates. Flooded batteries require maintenance but are typically the most economical option.
To convert watts to amps, divide the wattage by the system voltage. For DC systems: Amps = Watts ÷ Volts. For AC loads through an inverter, add 10-15% for inverter losses before calculating.