Battery Life Calculator

Battery life estimation starts with a simple formula: divide the battery capacity (mAh) by the average current draw (mA) to get runtime in hours. A 3000 mAh battery powering a 50 mA device lasts about 60 hours. But real-world battery life is always shorter than this ideal calculation.

Efficiency losses from voltage regulators (DC-DC converters, LDOs) reduce the usable capacity. A regulator operating at 85% efficiency means only 85% of the battery's stored energy reaches your circuit. Always factor in regulator efficiency for accurate estimates.

For IoT and low-power devices, the duty cycle approach is essential. Most IoT sensors spend 99%+ of their time in sleep mode (microamps) and only wake briefly to measure and transmit. The average current becomes I_avg = I_active x duty + I_sleep x (1-duty). Reducing active time or sleep current has a dramatic effect on battery life.

Self-discharge is the rate at which a battery loses charge even when disconnected. Lithium cells lose 1-3% per month; NiMH can lose 10-20% per month. For long-deployment IoT nodes, choose low-self-discharge cells. The C-rate of a battery indicates its maximum safe discharge current: 1C means the battery can deliver its full capacity in one hour (e.g., 2000 mAh at 2000 mA).

Battery Types

• LiPo (3.7V): High energy density, thin profile, 1-3% self-discharge/mo. Ideal for wearables and drones.
• Li-Ion 18650 (3.6V): 2000-3500 mAh, good cycle life, 1-2% self-discharge/mo. Standard for power banks and EVs.
• AA Alkaline (1.5V): ~2500 mAh, widely available, not rechargeable, low self-discharge (~2%/yr).
• AA NiMH (1.2V): ~2000 mAh rechargeable, 10-20% self-discharge/mo (low-self-discharge types ~1%/mo).
• CR2032 Coin Cell (3V): ~220 mAh, very low self-discharge (~1%/yr). Used in RTC, key fobs, and sensors.

Applications

• IoT sensor node deployment planning
• Wearable device runtime estimation
• Remote monitoring battery sizing
• Portable electronics design