Calculators · Power budget
Battery life
LiveEstimate battery runtime from capacity, load current, efficiency, and duty cycle.
Estimate runtime before choosing cells, regulators, and sleep modes.
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Calculator guide
Battery life formulas and practical checks
Formulas, examples, and practical notes for using the result with confidence.
Overview
Battery runtime is a budget: the battery brings a certain amount of charge, and every sensor reading, radio burst, LED, and regulator takes a nibble. The useful question is not just “how big is the battery?” but “what does the whole project draw on average?”
This battery life calculator combines capacity, load current, duty cycle, conversion efficiency, and usable-capacity derating. It gives a practical planning estimate before you commit to a battery holder, enclosure, or charging routine.
Current example
Enter valid values above and this example will update with the calculator state.
Capacity is the size of the tank
Ideal runtime is capacity divided by current, but real batteries rarely deliver the label value.
Battery capacity is usually stated in milliamp-hours. A 2000 mAh cell can theoretically deliver 200 mA for 10 hours, but discharge rate, cutoff voltage, age, and temperature change the useful capacity.
Use the load current that the battery actually sees. If a regulator is involved, the input current may not equal the output current.
Capacity in mAh is charge, not energy. When comparing batteries with different voltages, watt-hours are the fairer comparison because they include both voltage and capacity.
Ideal runtime
Sleeping projects still wake up hungry
Sleeping devices should be calculated from average current, not peak current alone.
A sensor node may draw high current while transmitting and microamps while sleeping. Duty cycle turns that changing load into an average current for a first estimate.
If the load has several states, calculate each state current multiplied by its time fraction, then add the results.
Measure short radio or motor bursts with equipment fast enough to catch them. A basic multimeter may average the spikes away even though the battery and regulator still have to supply them.
Duty-cycle average
Add a reality cushion
Converters, protection circuits, temperature, and cutoff voltage reduce practical runtime.
Boost and buck converters waste some energy. Entering efficiency increases the battery-side current required for a given load.
Usable capacity is a practical derating. It is useful when the battery cannot be discharged fully, when voltage sag matters, or when you want a conservative field estimate.
Weekend sensor node
A 2000 mAh pack with 80% usable capacity and a 10 mA average battery current has a planning estimate of about 160 hours, or 6.7 days.
Projects worth budgeting early
Runtime estimates are useful early, before the enclosure and battery choice are locked.
Use the calculator for IoT sensors, wearable prototypes, LED props, remote controls, data loggers, and portable test gear.
For production designs, validate with measured current profiles and real discharge tests using the intended battery chemistry.
Sleepy sensor nodes
Estimate the benefit of firmware sleep modes and lower transmit duty cycle.
Portable tools
Check whether a battery pack can support the required use time.
Regulator selection
Compare runtime impact from linear regulators, buck converters, and boost converters.
The sneaky loads that ruin runtime
The biggest runtime surprises come from hidden loads and optimistic battery assumptions.
Quiescent regulator current, power LEDs, sensor warm-up time, wireless bursts, and leakage can dominate low-power projects.
Battery capacity is normally measured under specified conditions. A different discharge current or temperature can produce a very different result.
Assumptions and limits
- Results are design estimates, not a substitute for datasheets, measurements, safety approvals, or engineering review.
- Component tolerance, temperature, supply variation, and real loading can move the final circuit away from the ideal calculation.
- Calculator results are estimates for design and learning. Verify values against datasheets, tolerances, temperature, load behaviour, and safety requirements before using them in a real circuit.
Licensing
Calculator copy, equations, and generated visuals are provided for learning and design-reference use on Kobee unless a specific licence is shown.
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