Battery Life Calculator
Estimate how long a battery lasts under a given load.
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How It Works
Calculates battery runtime using: Hours = Capacity (mAh) ÷ Current Draw (mA). A 2,000 mAh battery powering a 200 mA device lasts 10 hours theoretically. Real life is 70-80% of theoretical.
Formula
Life = Capacity / LoadQuick Reference
Common calculations — results you can verify instantly.
3000mAh, 100mA device
3000/100
30 hours (theoretical)
5000mAh, 500mA device
5000/500×0.8
8 hours (real)
Phone: 4000mAh, 200mA avg
4000/200×0.8
~16 hours
Tips & Shortcuts
Add 20-30% buffer: real-world efficiency is never 100%.
Lithium-ion should not be discharged below 20% for longevity.
Temperature significantly affects battery life: cold reduces capacity by 20-30%.
Common Mistakes
Using theoretical capacity without efficiency factor
Real battery life is typically 70-80% of theoretical. Apply a 0.7-0.8 efficiency multiplier.
Running lithium batteries to 0% regularly
Deep discharge shortens lithium battery lifespan. Keep between 20-80% for maximum cycles.
Frequently Asked Questions
A phone needs ~3,500 mAh. 10,000 × 0.8 efficiency = 8,000 effective mAh ÷ 3,500 ≈ 2.3 full charges.
Chemical reactions in batteries slow at low temperatures, reducing the effective charge capacity. Lithium-ion batteries lose ~20-30% capacity at 0°C.
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