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Calculate how long your battery will last based on its capacity in mAh and the device current consumption. Estimate total runtime, charge cycles per day, and years of battery life for any electronic device.
Battery life estimation is critical for portable electronics product development, IoT device design, and consumer electronics. Manufacturers spend significant engineering effort optimizing firmware to reduce average current draw — often achieving 2-5× longer battery life through software alone without changing hardware.
Battery life is determined by dividing the battery capacity (in milliamp-hours, mAh) by the device current consumption (in milliamps, mA). The result gives you the theoretical runtime in hours. In practice, actual battery life is 60-80% of theoretical due to chemistry inefficiencies, temperature effects, and the fact that batteries cannot be fully discharged.
mAh is the standard unit for battery capacity. A 3,000 mAh battery can theoretically supply 3,000 mA for 1 hour, or 1,000 mA for 3 hours, or 100 mA for 30 hours. Modern smartphone batteries range from 3,000-5,000 mAh. Laptop batteries are typically measured in Wh (watt-hours) = mAh × voltage / 1,000.
| Device | Capacity | Draw (mA avg) | Est. Life |
|---|---|---|---|
| iPhone 15 | 3,877 | ~20 | ~24 hr |
| Samsung Galaxy S24 | 4,000 | ~18 | ~25 hr |
| iPad Pro | 10,090 | ~50 | ~15 hr |
| MacBook Pro 14" | 70 Wh | — | ~18 hr |
| AirPods Pro | ~45 mAh each | ~5 | ~6 hr |
| AA Battery | 2,500 | ~200 | ~12 hr |
Different battery chemistries have vastly different characteristics that affect real-world runtime beyond simple mAh calculations. Understanding your battery type helps set accurate expectations and optimize usage patterns for maximum longevity.
Li-ion batteries (cylindrical cells like 18650) and Li-Po (pouch cells used in phones/laptops) both operate at 3.6-3.7V nominal. Li-Po cells can be made thinner and in custom shapes. Both have similar energy density (~150-250 Wh/kg) and the same cycle life characteristics. The theoretical mAh calculation applies equally to both.
Peukert's Law states that higher discharge rates reduce effective capacity. A battery rated at 3,000 mAh at C/10 rate (300mA) may only deliver 2,400 mAh at 1C rate (3,000mA) — 20% less. This is why heavy loads drain batteries faster than the simple mAh/mA formula predicts. The Peukert exponent is typically 1.1-1.3 for Li-ion.
Cold temperatures significantly reduce battery performance. At 0°C, Li-ion capacity drops 20-30%. At -20°C, capacity can be halved. This is why phones die quickly in winter despite showing 30% battery. Heat above 40°C accelerates permanent capacity degradation. Ideal storage temperature for Li-ion is 15-25°C at 40-50% charge.