Free battery life calculator. Estimate how long your device battery will last based on capacity (mAh/Wh) and power consumption (mA/W). Perfect for phones, laptops, IoT devices, and DIY projects.
Real-world batteries are typically 80-90% efficient
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Whether you're designing an IoT device, planning a camping trip, or just curious about your phone's battery, our calculator gives you accurate runtime estimates based on capacity and power draw.
Battery life depends on two factors: how much energy the battery stores (capacity) and how fast the device uses it (consumption). Capacity is measured in milliamp-hours (mAh) or watt-hours (Wh), while consumption is in milliamps (mA) or watts (W).
Battery Life Formula
Time (hours) = Capacity (mAh) ÷ Current (mA)Choose the right battery size for your project's power requirements.
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Real-world factors include: discharge efficiency (80-90%), voltage drop as battery depletes, temperature effects, and variable power consumption. Use 80-85% efficiency for realistic estimates.
mAh (milliamp-hours) measures charge capacity at a specific voltage. Wh (watt-hours) measures total energy regardless of voltage. Convert using: Wh = mAh × Voltage ÷ 1000.
Check device specifications, use a USB power meter, or estimate from typical values. Smartphones use 200-500mA active, laptops 15-60W, LED lights 1-20W.
Yes. Lithium batteries lose capacity over time - typically 20% after 500 charge cycles. A '5000mAh' battery might only hold 4000mAh after 2 years of heavy use.