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Battery Power Budget Planner

Estimate average current and battery runtime from duty cycles.

One load per row. Currents must be drawn from the battery itself.

mAh
%
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Try an example: Intermittent sensor

More about this tool

How it works

List active and sleep currents with duty cycles to estimate average draw and battery runtime.

  • Average each load as active current times duty fraction plus sleep current times remaining fraction. Sum the averages.
  • Divide usable battery capacity by total average battery current; zero current has no finite runtime estimate.

A planning estimate only. Capacity depends on discharge rate, temperature, aging and cutoff voltage. Account for converter losses and all loads in battery-side currents.

Sources

Part of Ohmforge

  • Ohmforge Virtual electronics workbench

    Draw a circuit, switch it on, and measure it with real-feeling bench instruments.

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How to use the Battery Power Budget Planner

Estimate average battery current and runtime from active and sleep loads, duty cycles and usable capacity.

What it is for

A device that sleeps most of the time can last much longer than an estimate based only on its active current suggests. This planner combines active and sleep currents with duty cycles to estimate the average battery-side current of each load and the combined runtime.

Enter each load as a comma-separated name, active current in milliamps, sleep current in milliamps and active duty percentage. Then enter battery capacity in milliamp-hours and the percentage you expect to be usable. Use currents drawn from the battery itself, including conversion losses where relevant.

The result is a planning estimate, not a battery guarantee. Capacity and performance vary with discharge rate, temperature, aging and cutoff voltage. Account for every load and verify the design with measurements.

Worked example

Enter these two loads:

Controller,20,0.1,10
Sensor,5,0.01,5

Set capacity to 2000 mAh and usable capacity to 80%. The controller averages 2.09 mA and the sensor averages 0.2595 mA. Together they draw 2.3495 mA on average.

The usable capacity is 1600 mAh. Dividing that by the total average gives Estimated runtime: 681.0 h (28.4 days) at an average of 2.3495 mA. This estimate assumes the stated currents and duty cycles remain representative over the discharge.

How to read the result

The load table shows the entered active and sleep currents, active duty and calculated average for each row. Compare the averages to find which load dominates the budget; a small sleep current can matter when a load spends most of its time asleep.

The metrics report total average current, usable capacity and the estimated runtime in hours and in days. If total average current is zero, the tool reports no finite runtime estimate rather than a numeric lifetime.

Tips and common mistakes

  • Measure or estimate current at the battery, not just at a regulated load.
  • Include regulators, indicators and other continuously powered circuits.
  • Express duty as the percentage of time active, between zero and 100.
  • Include sleep current even if it looks small compared with active current.
  • Choose a usable percentage that reflects your actual cutoff and operating conditions.
  • Recheck the estimate when the duty cycle or operating temperature changes.

FAQ

Does the planner account for converter efficiency?

Only if the currents you enter already reflect the battery-side draw, including those losses.

What happens at zero average current?

There is no finite runtime estimate because the model has no current consumption to divide into capacity.

Is the percentage a battery state of charge?

It is the fraction of the stated capacity you choose to treat as usable for this estimate. It is not a live battery measurement.

Does the result predict battery aging?

No. Aging and temperature can change usable capacity, so measure the real device and revisit the assumptions.

Guide last updated:

For scripts and AI agents

  • JSON API: POST https://ohmforgepowerbudget.usefulweb.site/api/v1/calculate (same calculation as this page)
  • Interface description: OpenAPI 3.1 · AI guide: llms.txt
  • MCP server (Streamable HTTP): https://ohmforgepowerbudget.usefulweb.site/mcp · tool name ohmforge_power_budget
Example request
curl -s -X POST https://ohmforgepowerbudget.usefulweb.site/api/v1/calculate \
  -H 'content-type: application/json' \
  -d '{"loads":"Controller,20,0.1,10\nSensor,5,0.01,5","capacity":2000,"usablePercent":80}'
Feedback · ideas & bug reports welcome