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
You might also find these calculators useful
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
Choose the right battery size for your project's power requirements.
Know if your devices will last through a flight, hike, or power outage.
Evaluate different battery and device combinations before purchasing.
Estimate screen-on time based on your phone's battery and usage patterns.
Calculate how many charges you'll get from your portable charger.
Size batteries for Arduino, ESP32, or Raspberry Pi projects.
Design off-grid power systems with appropriate battery banks.
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 ร Voltage รท 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.