Battery Runtime Calculator
Estimated Runtime (hours)
—
Runtime (minutes)
—
Battery Energy (Wh)
—
Device Power (W)
—
How to Calculate Battery Runtime
Basic battery runtime = capacity (mAh) / current draw (mA). A 5000 mAh battery powering a 500 mA device theoretically lasts 10 hours. In practice, we apply a 0.8 (80%) efficiency factor to account for voltage regulation losses, self-discharge, and battery aging.
Battery energy in watt-hours (Wh) = mAh × voltage / 1000. A 5000 mAh, 3.7V lithium battery stores 18.5 Wh. Airlines limit lithium batteries to 100 Wh for carry-on — this helps you check compliance.
Real-world runtime varies with temperature (cold reduces capacity), discharge rate (high draw reduces effective capacity via Peukert's effect), age (batteries lose capacity over charge cycles), and voltage regulation efficiency. This calculator provides a practical estimate with the 80% factor.
Frequently Asked Questions
How do I calculate battery life?
Hours = (mAh / mA) × 0.8. The 0.8 factor accounts for real-world inefficiencies. A 3000 mAh battery at 200 mA lasts about 12 hours.
What is mAh?
Milliamp-hours — a unit of electric charge. It represents how many milliamps a battery can supply for one hour. Higher mAh = longer runtime.
Why does my battery not last as long as calculated?
Real-world factors: efficiency losses, age degradation, temperature effects, variable current draw, and the Peukert effect at high discharge rates.
How many charge cycles does a battery last?
Lithium-ion batteries typically last 300-500 full charge cycles before capacity drops to 80%. Partial charges count proportionally (two 50% charges ≈ one full cycle).