Documentation sections

Battery Life Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug battery-life. Estimate battery runtime for IoT and portable devices given average current draw, duty cycle, self-discharge rate, and depth-of-discharge cutoff. Suitable for LiPo, alkaline, NiMH, and coin-cell batteries.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of battery-life
Name	Unit	Range	Default	Description
capacitynumber	mAh	1 … 100000	2000	Battery Capacity
avgCurrentnumber	mA	0.001 … 10000	100	Average current drawn by the device during active operation
dutyCyclenumber	%	0.001 … 100	100	Percentage of time the device is active and drawing current. 100% = continuous operation.
selfDischargenumber	%/month	0 … 30	2	Monthly self-discharge rate of the battery. LiPo: ~2%, NiMH: ~15%, Alkaline: ~1%
cutoffSocnumber	%	0 … 80	20	Minimum state of charge at which the device stops operating. 20% = device shuts off with 20% capacity remaining.
numLoadsnumber	none	0 … 7	0	Loads on the battery beside the device, each with its own current and duty cycle (0–7)
load1Currentnumber	mA	0 … 10000	10	Current additional load 1 draws while it is on
load1Dutynumber	%	0 … 100	10	Share of the time additional load 1 is on
load2Currentnumber	mA	0 … 10000	10	Current additional load 2 draws while it is on
load2Dutynumber	%	0 … 100	10	Share of the time additional load 2 is on
load3Currentnumber	mA	0 … 10000	10	Current additional load 3 draws while it is on
load3Dutynumber	%	0 … 100	10	Share of the time additional load 3 is on
load4Currentnumber	mA	0 … 10000	10	Current additional load 4 draws while it is on
load4Dutynumber	%	0 … 100	10	Share of the time additional load 4 is on
load5Currentnumber	mA	0 … 10000	10	Current additional load 5 draws while it is on
load5Dutynumber	%	0 … 100	10	Share of the time additional load 5 is on
load6Currentnumber	mA	0 … 10000	10	Current additional load 6 draws while it is on
load6Dutynumber	%	0 … 100	10	Share of the time additional load 6 is on
load7Currentnumber	mA	0 … 10000	10	Current additional load 7 draws while it is on
load7Dutynumber	%	0 … 100	10	Share of the time additional load 7 is on

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of battery-life
Field	Unit	Description
runtimeHoursheadline	h	Estimated battery runtime in hours
runtimeDays	days	Estimated battery runtime in days
effectiveCurrent	mA	Average current after applying duty cycles: the device plus every additional load, before self-discharge
usableCapacityMAh	mAh	Capacity available after accounting for the cutoff state of charge
selfDischargeCurrent	mA	The battery’s self-discharge as an equivalent current: capacity × rate per month / 720 h

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "battery-life",
    "inputs": {
      "capacity": 2000,
      "avgCurrent": 100,
      "dutyCycle": 100,
      "selfDischarge": 2,
      "cutoffSoc": 20,
      "numLoads": 0,
      "load1Current": 10,
      "load1Duty": 10,
      "load2Current": 10,
      "load2Duty": 10,
      "load3Current": 10,
      "load3Duty": 10,
      "load4Current": 10,
      "load4Duty": 10,
      "load5Current": 10,
      "load5Duty": 10,
      "load6Current": 10,
      "load6Duty": 10,
      "load7Current": 10,
      "load7Duty": 10
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("battery-life", {
    "capacity": 2000,
    "avgCurrent": 100,
    "dutyCycle": 100,
    "selfDischarge": 2,
    "cutoffSoc": 20,
    "numLoads": 0,
    "load1Current": 10,
    "load1Duty": 10,
    "load2Current": 10,
    "load2Duty": 10,
    "load3Current": 10,
    "load3Duty": 10,
    "load4Current": 10,
    "load4Duty": 10,
    "load5Current": 10,
    "load5Duty": 10,
    "load6Current": 10,
    "load6Duty": 10,
    "load7Current": 10,
    "load7Duty": 10,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "battery-life",
    "inputs": {
      "capacity": 2000,
      "avgCurrent": 100,
      "dutyCycle": 100,
      "selfDischarge": 2,
      "cutoffSoc": 20,
      "numLoads": 0,
      "load1Current": 10,
      "load1Duty": 10,
      "load2Current": 10,
      "load2Duty": 10,
      "load3Current": 10,
      "load3Duty": 10,
      "load4Current": 10,
      "load4Duty": 10,
      "load5Current": 10,
      "load5Duty": 10,
      "load6Current": 10,
      "load6Duty": 10,
      "load7Current": 10,
      "load7Duty": 10
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "battery-life",
	  "inputs": {
	    "capacity": 2000,
	    "avgCurrent": 100,
	    "dutyCycle": 100,
	    "selfDischarge": 2,
	    "cutoffSoc": 20,
	    "numLoads": 0,
	    "load1Current": 10,
	    "load1Duty": 10,
	    "load2Current": 10,
	    "load2Duty": 10,
	    "load3Current": 10,
	    "load3Duty": 10,
	    "load4Current": 10,
	    "load4Duty": 10,
	    "load5Current": 10,
	    "load5Duty": 10,
	    "load6Current": 10,
	    "load6Duty": 10,
	    "load7Current": 10,
	    "load7Duty": 10
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "battery-life",
  "values": {
    "runtimeHours": 15.991116046640755,
    "runtimeDays": 0.6662965019433648,
    "effectiveCurrent": 100,
    "usableCapacityMAh": 1600,
    "selfDischargeCurrent": 0.05555555555555555
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:battery-life",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Nordic Semiconductor PWR Profiler methodology; Texas Instruments SLUA364",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "capacity": {
          "min": 1,
          "max": 100000,
          "unit": "mAh"
        },
        "avgCurrent": {
          "min": 0.001,
          "max": 10000,
          "unit": "mA"
        },
        "dutyCycle": {
          "min": 0.001,
          "max": 100,
          "unit": "%"
        },
        "selfDischarge": {
          "min": 0,
          "max": 30,
          "unit": "%/month"
        },
        "cutoffSoc": {
          "min": 0,
          "max": 80,
          "unit": "%"
        },
        "numLoads": {
          "min": 0,
          "max": 7,
          "unit": ""
        },
        "load1Current": {
          "min": 0,
          "max": 10000,
          "unit": "mA"
        },
        "load1Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load2Current": {
          "min": 0,
          "max": 10000,
          "unit": "mA"
        },
        "load2Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load3Current": {
          "min": 0,
          "max": 10000,
          "unit": "mA"
        },
        "load3Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load4Current": {
          "min": 0,
          "max": 10000,
          "unit": "mA"
        },
        "load4Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load5Current": {
          "min": 0,
          "max": 10000,
          "unit": "mA"
        },
        "load5Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load6Current": {
          "min": 0,
          "max": 10000,
          "unit": "mA"
        },
        "load6Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load7Current": {
          "min": 0,
          "max": 10000,
          "unit": "mA"
        },
        "load7Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "capacity": 2000,
      "avgCurrent": 100,
      "dutyCycle": 100,
      "selfDischarge": 2,
      "cutoffSoc": 20,
      "numLoads": 0,
      "load1Current": 10,
      "load1Duty": 10,
      "load2Current": 10,
      "load2Duty": 10,
      "load3Current": 10,
      "load3Duty": 10,
      "load4Current": 10,
      "load4Duty": 10,
      "load5Current": 10,
      "load5Duty": 10,
      "load6Current": 10,
      "load6Duty": 10,
      "load7Current": 10,
      "load7Duty": 10
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "capacity"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageBattery Life Calculator, at these values