Battery Life Calculator
Estimate battery runtime for your project. Account for duty cycles and efficiency factors.
Calculator
LDO: 70-90%, Buck: 85-95%, Direct: 100%
Time active vs sleep (100% = always on)
Battery Life (hours) = (Capacity × Efficiency) / (Current × Duty Cycle)
How to Use This Calculator
This battery life calculator estimates how long your device will run on a given battery based on current consumption, regulator efficiency, and duty cycle.
- Select or Enter Battery Capacity — Click a common battery or enter custom mAh
- Enter Load Current — The current your circuit draws when active
- Set Regulator Efficiency — Account for power conversion losses (100% for direct battery)
- Set Duty Cycle — Percentage of time the device is active vs sleeping
- Click Calculate — See estimated battery life in hours, days, or months
The Battery Life Formula
Battery life is calculated by dividing the battery's capacity by the average current draw, accounting for regulator efficiency and duty cycle.
Understanding Each Factor
- Battery Capacity: Total charge storage, typically in milliamp-hours (mAh). A 2000mAh battery can deliver 2000mA for 1 hour, or 200mA for 10 hours.
- Regulator Efficiency: How much battery power reaches your circuit. An 85% efficient regulator wastes 15% as heat.
- Duty Cycle: The fraction of time the device is active. A device that sleeps 90% of the time has a 10% duty cycle.
Common Battery Types
| Battery | Capacity | Voltage | Best For |
|---|---|---|---|
| CR2032 | 225 mAh | 3V | Low-power sensors, RTC backup |
| AAA | 1200 mAh | 1.5V | Remote controls, small devices |
| AA | 2800 mAh | 1.5V | General purpose, medium current |
| 18650 Li-ion | 2600 mAh | 3.7V | High current, rechargeable |
| LiPo 1S | 500-2000 mAh | 3.7V | Drones, wearables, IoT |
Capacity Varies with Discharge Rate
Battery capacity ratings assume a specific discharge rate (often C/20). Drawing higher currents reduces effective capacity. A 2000mAh battery might only deliver 1800mAh at high discharge rates.
Optimization Tips
Reduce Active Current
- Lower CPU clock speed when full speed isn't needed
- Turn off unused peripherals (WiFi, Bluetooth, GPS)
- Use hardware sleep modes during idle periods
- Choose efficient voltage regulators (buck over LDO)
Implement Sleep Modes
- Light Sleep: Quick wake-up, moderate power savings
- Deep Sleep: Longer wake-up, significant power savings
- Hibernation: Minimal power, requires full reboot
Optimize Duty Cycle
- Send data in batches instead of continuously
- Use interrupts instead of polling
- Increase sleep intervals when possible
- Use RTC wake-up instead of timer loops
Example: ESP32 Power Optimization
| Active (WiFi TX) | ~240 mA |
| Active (CPU only) | ~30 mA |
| Light Sleep | ~0.8 mA |
| Deep Sleep | ~10 µA |
Frequently Asked Questions
Why is my actual battery life shorter than calculated?
Several factors reduce real-world battery life: battery self-discharge, temperature effects, battery aging, peak current demands, and inrush currents during wake-up. Use the calculated value as an optimistic estimate and apply a safety factor of 70-80%.
What efficiency should I use?
Direct connection (no regulator): 100%
LDO regulator: (Vout/Vin) × 100, typically 60-80%
Buck converter: 85-95%
Boost converter: 80-90%
How do I measure actual current consumption?
Use a multimeter in series with the battery for average current. For sleep/wake cycles, use an oscilloscope with a current probe or a specialized power profiler (like Nordic PPK or Qoitech Otii).
Can I use this for rechargeable batteries?
Yes, the calculation works for any battery type. Note that rechargeable batteries have lower capacity than their ratings suggest after many charge cycles. Li-ion batteries typically retain 80% capacity after 300-500 cycles.
How does temperature affect battery life?
Cold temperatures reduce battery capacity significantly (up to 50% at -20°C). Hot temperatures increase self-discharge and accelerate battery degradation. Design for the expected operating temperature range.
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