Battery Life Calculator
Estimate battery runtime from capacity, current draw, efficiency, and self-discharge rate.
Component Values
Results
Battery discharge over time
How to estimate battery life accurately
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).
Continuous Mode
Life (h) = Capacity (mAh) / Current (mA)Duty Cycle Average Current
I_avg = I_active x D + I_sleep x (1-D)With Efficiency
Life = (Capacity x Eff%) / I_avgBattery 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
Battery Chemistry Reference
| Chemistry | Nominal V | Energy (Wh/kg) | Self-discharge/mo | Cycle Life |
|---|---|---|---|---|
| Li-ion | 3.7V | 150–200 | 2–3% | 300–500 |
| LiPo | 3.7V | 130–200 | 2–5% | 300–500 |
| LiFePO4 | 3.2V | 90–120 | 1–3% | 2000+ |
| Alkaline | 1.5V | 100–150 | 0.3%/yr | Primary |
| NiMH | 1.2V | 60–120 | 15–30% | 500–1000 |
| Lead-acid | 2.0V | 30–50 | 3–5% | 200–300 |
Design Examples
Battery: 2000mAh Li-ion. Active: 80mA for 0.1s/min. Sleep: 20µA the rest of the time.
Avg current ≈ 153 µA · Life ≈ 2000/0.153 = 13,071h ≈ 1.5 years
Battery: 9V alkaline (550mAh). Total draw: 70mA. Alkaline derating factor: 0.7.
Life = 550/70 × 0.7 ≈ 5.5 hours
CR2032 = 240mAh capacity. Average current draw ≈ 11.7µA from periodic TX bursts + deep sleep baseline.
Life ≈ 240/0.0117 ≈ 20,500h ≈ 2.3 years
Battery life formula
t = (C × η) / I_avg
C = capacity (mAh) · η = efficiency (0.7–0.85 alkaline/NiMH, 0.9–0.95 Li-ion)
For pulsed loads: I_avg = (I_active × t_active + I_sleep × t_sleep) / t_totalDid you know? The energy density of Li-ion batteries has improved roughly 3× since their commercialization in 1991. Despite this, Li-ion still stores about 150–200 Wh/kg — less than 1% of the energy density of gasoline (12,000 Wh/kg). This gap drives ongoing battery research.