Documentation sections

Battery Charge Time Calculator

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

Slug battery-charge-time. Calculate Li-ion battery charge time using CC/CV method, including CC phase duration, total charge time, energy input, and charging efficiency

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-charge-time
Name	Unit	Range	Default	Description
capacitynumber	mAh	at least 1	3000	Rated battery capacity in mAh
chargeCurrentCnumber	C	0.1 … 4	1	Charge current as a multiple of battery capacity (1C = full capacity in 1 hour)
initialSocnumber	%	0 … 99	20	Initial State of Charge
targetSocnumber	%	1 … 100	80	Target State of Charge
chargingVoltagenumber	V	at least 0.1	4.2	Terminal voltage during charging
battVoltagenumber	V	at least 0.1	3.7	Nominal battery voltage for energy calculation
requiredTimenumber	hr	at least 0.01	3	The time the charge must finish in. 3 h is the upper end of a full Li-ion charge at 0.5C to 1C (Battery University BU-409: about 2–3 hours)

Outputs

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

Outputs of battery-charge-time
Field	Unit	Description
chargeTimeheadline	hr	Total Charge Time
ccTime	hr	CC Phase Time
chargeCurrent	mA	Charge Current
energyIn	mWh	Energy Input
chargingEfficiency	%	Charging Efficiency

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-charge-time",
    "inputs": {
      "capacity": 3000,
      "chargeCurrentC": 1,
      "initialSoc": 20,
      "targetSoc": 80,
      "chargingVoltage": 4.2,
      "battVoltage": 3.7,
      "requiredTime": 3
    }
  }'

import rftools

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

result = client.calculate("battery-charge-time", {
    "capacity": 3000,
    "chargeCurrentC": 1,
    "initialSoc": 20,
    "targetSoc": 80,
    "chargingVoltage": 4.2,
    "battVoltage": 3.7,
    "requiredTime": 3,
})
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-charge-time",
    "inputs": {
      "capacity": 3000,
      "chargeCurrentC": 1,
      "initialSoc": 20,
      "targetSoc": 80,
      "chargingVoltage": 4.2,
      "battVoltage": 3.7,
      "requiredTime": 3
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "battery-charge-time",
	  "inputs": {
	    "capacity": 3000,
	    "chargeCurrentC": 1,
	    "initialSoc": 20,
	    "targetSoc": 80,
	    "chargingVoltage": 4.2,
	    "battVoltage": 3.7,
	    "requiredTime": 3
	  }
	}`)
	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-charge-time",
  "values": {
    "chargeCurrent": 3000,
    "ccTime": 0.6,
    "chargeTime": 0.6,
    "energyIn": 7560,
    "chargingEfficiency": 88.09523809523809
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:battery-charge-time",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "capacity": {
          "min": 1,
          "max": null,
          "unit": "mAh"
        },
        "chargeCurrentC": {
          "min": 0.1,
          "max": 4,
          "unit": "C"
        },
        "initialSoc": {
          "min": 0,
          "max": 99,
          "unit": "%"
        },
        "targetSoc": {
          "min": 1,
          "max": 100,
          "unit": "%"
        },
        "chargingVoltage": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "battVoltage": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "requiredTime": {
          "min": 0.01,
          "max": null,
          "unit": "hr"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "capacity": 3000,
      "chargeCurrentC": 1,
      "initialSoc": 20,
      "targetSoc": 80,
      "chargingVoltage": 4.2,
      "battVoltage": 3.7,
      "requiredTime": 3
    },
    "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 Charge Time Calculator, at these values