Battery Life Calculator
Estimate how long a battery will last based on capacity and load current.
Results
Battery life depends on capacity (mAh) and current draw (mA). This calculator gives a theoretical maximum runtime - real-world performance varies based on temperature, discharge rate and battery age. The energy calculation assumes a 3.7V nominal lithium-ion cell, the most common chemistry in phones, laptops and portable electronics.
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Frequently asked questions
3000 / 150 = 20 hours. In practice expect 15-17 hours due to efficiency losses, voltage regulation and battery aging reducing effective capacity by 15-25%.
Divide battery capacity (mAh) by average current draw (mA). A 2000 mAh battery powering a 50 mA circuit lasts 40 hours theoretically, about 32-34 hours in practice.
Milliamp-hours (mAh) is a measure of charge capacity. A 3000 mAh battery can deliver 3000 mA for 1 hour, 300 mA for 10 hours or 150 mA for 20 hours.
Multiply mAh by nominal voltage and divide by 1000. A 3000 mAh lithium battery at 3.7V = 11.1 Wh. This is the standard capacity measure used for shipping regulations.
Voltage regulators waste 5-15% of energy as heat. Battery capacity drops 20% at 0°C and decreases 20% after 500 charge cycles. High discharge rates also reduce effective capacity.