Documentation sections

Battery Runtime (Motor Load)

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

Slug battery-runtime-motor. Calculate battery runtime for motor-driven systems accounting for motor current draw, efficiency, and depth of discharge.

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-runtime-motor
Name	Unit	Range	Default	Description
batteryCapacityMahnumber	mAh	at least 1	2000	Battery Capacity
batteryVoltagenumber	V	at least 0.5	3.7	Battery Voltage
motorCurrentAnumber	A	at least 0.001	0.5	Motor Current (avg)
efficiencynumber	%	10 … 100	85	Motor driver + motor combined efficiency
depthOfDischargenumber	%	1 … 100	80	Depth of Discharge
motorDutynumber	%	1 … 100	100	Share of the time the motor runs at its average current. 100% = continuous.
numLoadsnumber	none	0 … 5	0	Loads on the battery beside the motor: more motors, servos, a controller board (0–5)
load1Currentnumber	A	0 … 100	0.5	Average current additional load 1 draws while on, referred to the battery voltage
load1Dutynumber	%	0 … 100	100	Share of the time additional load 1 is on
load1Efficiencynumber	%	10 … 100	85	Efficiency of the drive or converter between the battery and additional load 1
load2Currentnumber	A	0 … 100	0.5	Average current additional load 2 draws while on, referred to the battery voltage
load2Dutynumber	%	0 … 100	100	Share of the time additional load 2 is on
load2Efficiencynumber	%	10 … 100	85	Efficiency of the drive or converter between the battery and additional load 2
load3Currentnumber	A	0 … 100	0.5	Average current additional load 3 draws while on, referred to the battery voltage
load3Dutynumber	%	0 … 100	100	Share of the time additional load 3 is on
load3Efficiencynumber	%	10 … 100	85	Efficiency of the drive or converter between the battery and additional load 3
load4Currentnumber	A	0 … 100	0.5	Average current additional load 4 draws while on, referred to the battery voltage
load4Dutynumber	%	0 … 100	100	Share of the time additional load 4 is on
load4Efficiencynumber	%	10 … 100	85	Efficiency of the drive or converter between the battery and additional load 4
load5Currentnumber	A	0 … 100	0.5	Average current additional load 5 draws while on, referred to the battery voltage
load5Dutynumber	%	0 … 100	100	Share of the time additional load 5 is on
load5Efficiencynumber	%	10 … 100	85	Efficiency of the drive or converter between the battery and additional load 5

Outputs

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

Outputs of battery-runtime-motor
Field	Unit	Description
runtimeHoursheadline	h	Runtime
runtimeMinutes	min	Runtime
usableCapacityMah	mAh	Usable Capacity
energyWh	Wh	Battery Energy (est.)
batteryCurrent	A	Average current drawn from the battery: each load’s current × duty cycle ÷ its efficiency, summed

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-runtime-motor",
    "inputs": {
      "batteryCapacityMah": 2000,
      "batteryVoltage": 3.7,
      "motorCurrentA": 0.5,
      "efficiency": 85,
      "depthOfDischarge": 80,
      "motorDuty": 100,
      "numLoads": 0,
      "load1Current": 0.5,
      "load1Duty": 100,
      "load1Efficiency": 85,
      "load2Current": 0.5,
      "load2Duty": 100,
      "load2Efficiency": 85,
      "load3Current": 0.5,
      "load3Duty": 100,
      "load3Efficiency": 85,
      "load4Current": 0.5,
      "load4Duty": 100,
      "load4Efficiency": 85,
      "load5Current": 0.5,
      "load5Duty": 100,
      "load5Efficiency": 85
    }
  }'

import rftools

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

result = client.calculate("battery-runtime-motor", {
    "batteryCapacityMah": 2000,
    "batteryVoltage": 3.7,
    "motorCurrentA": 0.5,
    "efficiency": 85,
    "depthOfDischarge": 80,
    "motorDuty": 100,
    "numLoads": 0,
    "load1Current": 0.5,
    "load1Duty": 100,
    "load1Efficiency": 85,
    "load2Current": 0.5,
    "load2Duty": 100,
    "load2Efficiency": 85,
    "load3Current": 0.5,
    "load3Duty": 100,
    "load3Efficiency": 85,
    "load4Current": 0.5,
    "load4Duty": 100,
    "load4Efficiency": 85,
    "load5Current": 0.5,
    "load5Duty": 100,
    "load5Efficiency": 85,
})
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-runtime-motor",
    "inputs": {
      "batteryCapacityMah": 2000,
      "batteryVoltage": 3.7,
      "motorCurrentA": 0.5,
      "efficiency": 85,
      "depthOfDischarge": 80,
      "motorDuty": 100,
      "numLoads": 0,
      "load1Current": 0.5,
      "load1Duty": 100,
      "load1Efficiency": 85,
      "load2Current": 0.5,
      "load2Duty": 100,
      "load2Efficiency": 85,
      "load3Current": 0.5,
      "load3Duty": 100,
      "load3Efficiency": 85,
      "load4Current": 0.5,
      "load4Duty": 100,
      "load4Efficiency": 85,
      "load5Current": 0.5,
      "load5Duty": 100,
      "load5Efficiency": 85
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "battery-runtime-motor",
	  "inputs": {
	    "batteryCapacityMah": 2000,
	    "batteryVoltage": 3.7,
	    "motorCurrentA": 0.5,
	    "efficiency": 85,
	    "depthOfDischarge": 80,
	    "motorDuty": 100,
	    "numLoads": 0,
	    "load1Current": 0.5,
	    "load1Duty": 100,
	    "load1Efficiency": 85,
	    "load2Current": 0.5,
	    "load2Duty": 100,
	    "load2Efficiency": 85,
	    "load3Current": 0.5,
	    "load3Duty": 100,
	    "load3Efficiency": 85,
	    "load4Current": 0.5,
	    "load4Duty": 100,
	    "load4Efficiency": 85,
	    "load5Current": 0.5,
	    "load5Duty": 100,
	    "load5Efficiency": 85
	  }
	}`)
	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-runtime-motor",
  "values": {
    "usableCapacityMah": 1600,
    "runtimeHours": 2.7199999999999998,
    "runtimeMinutes": 163.2,
    "energyWh": 7.4,
    "batteryCurrent": 0.5882352941176471
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:battery-runtime-motor",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "batteryCapacityMah": {
          "min": 1,
          "max": null,
          "unit": "mAh"
        },
        "batteryVoltage": {
          "min": 0.5,
          "max": null,
          "unit": "V"
        },
        "motorCurrentA": {
          "min": 0.001,
          "max": null,
          "unit": "A"
        },
        "efficiency": {
          "min": 10,
          "max": 100,
          "unit": "%"
        },
        "depthOfDischarge": {
          "min": 1,
          "max": 100,
          "unit": "%"
        },
        "motorDuty": {
          "min": 1,
          "max": 100,
          "unit": "%"
        },
        "numLoads": {
          "min": 0,
          "max": 5,
          "unit": ""
        },
        "load1Current": {
          "min": 0,
          "max": 100,
          "unit": "A"
        },
        "load1Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load1Efficiency": {
          "min": 10,
          "max": 100,
          "unit": "%"
        },
        "load2Current": {
          "min": 0,
          "max": 100,
          "unit": "A"
        },
        "load2Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load2Efficiency": {
          "min": 10,
          "max": 100,
          "unit": "%"
        },
        "load3Current": {
          "min": 0,
          "max": 100,
          "unit": "A"
        },
        "load3Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load3Efficiency": {
          "min": 10,
          "max": 100,
          "unit": "%"
        },
        "load4Current": {
          "min": 0,
          "max": 100,
          "unit": "A"
        },
        "load4Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load4Efficiency": {
          "min": 10,
          "max": 100,
          "unit": "%"
        },
        "load5Current": {
          "min": 0,
          "max": 100,
          "unit": "A"
        },
        "load5Duty": {
          "min": 0,
          "max": 100,
          "unit": "%"
        },
        "load5Efficiency": {
          "min": 10,
          "max": 100,
          "unit": "%"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "batteryCapacityMah": 2000,
      "batteryVoltage": 3.7,
      "motorCurrentA": 0.5,
      "efficiency": 85,
      "depthOfDischarge": 80,
      "motorDuty": 100,
      "numLoads": 0,
      "load1Current": 0.5,
      "load1Duty": 100,
      "load1Efficiency": 85,
      "load2Current": 0.5,
      "load2Duty": 100,
      "load2Efficiency": 85,
      "load3Current": 0.5,
      "load3Duty": 100,
      "load3Efficiency": 85,
      "load4Current": 0.5,
      "load4Duty": 100,
      "load4Efficiency": 85,
      "load5Current": 0.5,
      "load5Duty": 100,
      "load5Efficiency": 85
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "batteryCapacityMah"
      ],
      "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 Runtime (Motor Load), at these values