Battery Runtime Calculator
Estimate runtime for real battery-powered electronics with Active, Idle, and Sleep load states. This calculator is designed for MCU, BLE, LoRa, Zigbee, GPS tracker, wearable, remote, smart lock, and low-power sensor duty-cycle analysis.
Use BAT-001 for a quick capacity divided by current estimate. Use this BAT-006 calculator when the current changes across operating states and a time-weighted average current is needed.
Engineering tool
Battery Runtime Calculator
Calculate average current, battery runtime, or required capacity for Active, Idle, and Sleep duty-cycle load profiles.
Rated battery capacity before usable-capacity derating.
Estimated usable portion of rated capacity under real conditions.
Operating States
Active
Current during radio transmit, sensing, GPS, motor movement, or MCU active work.
Percentage of total time spent in this state.
Idle
Current during standby, connected idle, waiting, or light processing.
Percentage of total time spent in this state.
Sleep
Current during deep sleep, shutdown, or low-power retention.
Percentage of total time spent in this state.
Battery Runtime
3.3721 weeks
3 wk 2 d 14 h 31 min
Result console
- Average current
- 4.766mA
- Average current
- 4.766mA
- Average current
- 4,766µA
- Duty cycle total
- 100%
- Usable capacity
- 2.7Ah
- Battery runtime
- 3.3721weeks
- Battery runtime decimal hours
- 566.512798993h
- Battery runtime human-readable
- 3 wk 2 d 14 h 31 min
- Usable capacity factor
- 90%
- Formula used
- t = Crated × Fu / Iavg
Duty-cycle requirement
Active, Idle, and Sleep duty cycles must total exactly 100%. Use time-weighted current when the device has additional states or variable load behavior.
This calculator uses a three-state time-weighted average current model. Real runtime depends on battery chemistry, cutoff voltage, temperature, aging, self-discharge, load transients, and converter efficiency.
Formula reference
Battery Runtime Duty-Cycle Formulas
Battery runtime uses Active, Idle, and Sleep state currents weighted by duty cycle. Currents use amperes, capacity uses amp-hours, runtime uses hours, and duty cycle uses 0 to 1 fractions.
Iavg = Iactive × Dactive + Iidle × Didle + Isleep × DsleepCusable = Crated × Fut = Cusable / IavgCrated = Iavg × t / FuVariable definitions
- Iavg
- Time-weighted average current
- Iactive
- Current during active work
- Iidle
- Current during idle or standby operation
- Isleep
- Current during sleep or low-power retention
- Dactive, Didle, Dsleep
- Duty cycle fractions for each state
- Crated
- Rated battery capacity
- Fu
- Usable capacity factor
- Cusable
- Usable battery capacity
- t
- Runtime in hours
Worked Examples
BLE Beacon
Active 15 mA at 1%, idle 1 mA at 4%, sleep 5 µA at 95%
Average current = 0.19475 mA; a 1000 mAh battery at 90% usable capacity gives about 4621 h.
Wireless Sensor
Active 25 mA at 2%, idle 0.8 mA at 8%, sleep 10 µA at 90%
Average current = 0.573 mA; a 2400 mAh battery at 85% usable capacity gives about 3560 h.
LoRa Node
Transmit 120 mA at 0.5%, idle 2 mA at 4.5%, sleep 15 µA at 95%
Average current ≈ 0.704 mA; a 5000 mAh battery at 90% usable capacity gives about 6390 h.
GPS Tracker
Active 100 mA at 10%, idle 10 mA at 20%, sleep 200 µA at 70%
Average current = 12.14 mA; a 3000 mAh battery at 90% usable capacity gives about 222 h.
Smart Lock
Motor/radio 250 mA at 0.2%, idle 3 mA at 9.8%, sleep 30 µA at 90%
Average current ≈ 0.821 mA; a 6000 mAh battery at 80% usable capacity gives about 5847 h.
Ultra-Low-Power MCU
Active 5 mA at 0.1%, idle 50 µA at 4.9%, sleep 1 µA at 95%
Average current = 8.4 µA; a 220 mAh battery at 85% usable capacity gives about 22,262 h.
Engineering Notes
Average Current
Average current is the time-weighted equivalent load current over a complete operating cycle.
Duty Cycle
Duty cycle describes how much time the device spends in each state. The three state percentages must total 100%.
Sleep Current
Sleep current can dominate long-life products because it is present for most of the operating time.
Standby Current
Idle or standby current should be included when the device remains connected, waiting, or periodically checking events.
Battery Runtime
Runtime is usable capacity divided by average current, before adding product-specific reserve margins.
Usable Capacity
Usable capacity can be lower than rated capacity because of cutoff voltage, temperature, aging, and discharge-rate effects.
Battery Self-Discharge
Long-duration designs must include battery self-discharge and leakage paths.
Battery Aging
Aging reduces usable capacity, especially after many cycles or long storage at high temperature.
Temperature
Cold temperature can reduce usable capacity and voltage performance.
Power Saving Modes
MCU, radio, sensor, and regulator low-power modes can reduce average current dramatically.
Always-On Systems
Always-on loads must be included even if they look small compared with active current.
Wireless Duty Cycling
Radio transmit and receive windows are often short, but the current can be high.
MCU Low Power Modes
Deep sleep, retention, RTC, and wake-source current should be measured on the final hardware.
Common Mistakes
Using peak current as average current
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Entering duty cycles that do not total 100%
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Ignoring sleep current
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Ignoring battery aging
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Ignoring low-temperature capacity loss
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Confusing µA with mA
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Confusing mAh with mA
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Ignoring always-on regulator or sensor current
Measure real current in each state and verify the duty cycle on final firmware before relying on a runtime estimate.
Support reference
FAQ
How do I calculate average current?
Multiply each state current by its duty-cycle fraction, then add the weighted currents. The duty cycles must total 100%.
How is duty cycle used?
Duty cycle represents the percentage of time spent in each state. A high-current active state can have a small runtime impact if its duty cycle is very low.
Why is sleep current important?
Sleep current dominates long-life products because the device may spend most of its time asleep. A few microamps can matter over months or years.
How do I estimate battery runtime?
Calculate average current from the load states, multiply rated capacity by the usable capacity factor, then divide usable capacity by average current.
How much does battery aging affect runtime?
Battery aging reduces usable capacity through cycle wear and calendar aging. Add design margin and verify runtime with aged batteries when reliability matters.
Can I ignore idle current?
Only if idle duty cycle is negligible or idle current is much smaller than the other weighted states. Otherwise idle current can materially affect average current.
Should I use rated or usable battery capacity?
Use rated capacity for datasheet comparison, then apply a usable capacity factor for cutoff voltage, temperature, aging, self-discharge, and load-rate effects.
Why is my real battery life shorter?
Real runtime can be shorter because of battery chemistry, cutoff voltage, voltage sag, temperature, aging, self-discharge, converter losses, wake events, and unmodeled loads.
Related Engineering Guides
Planned Engineering Guide
Average Current Explained
Planned Engineering Guide
Duty Cycle Calculation
Planned Engineering Guide
Low Power Design
Planned Engineering Guide
Battery Runtime Optimization
Planned Engineering Guide
Battery Capacity Planning
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Engineering Disclaimer
This calculator provides a first-pass runtime estimate. Validate the real system with measured current, firmware duty cycle, regulator efficiency, battery cutoff voltage, battery aging, temperature, and manufacturer battery data before final design decisions.