How to interpret battery level

[ibrahim-delice]

Prerequisites

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• [ x] I am running the latest version
• [ x] I checked the documentation and found no answer
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Question

I am reading the battery level from a device but do not know how to interpret the battery level percentages from the response.

This is how I read the characteristic:

const batteryChar = await device.readCharacteristicForService(
          '0000180F-0000-1000-8000-00805f9b34fb',
          '00002a19-0000-1000-8000-00805f9b34fb',
        );

Response:

{
  "id": 10789092832,
  "uuid": "00002a19-0000-1000-8000-00805f9b34fb",
  "isNotifiable": true,
  "isNotifying": true,
  "isReadable": true,
  "isWritableWithResponse": false,
  "serviceID": 10738251328,
  "value": "ZA==",
  "isIndicatable": false,
  "serviceUUID": "0000180f-0000-1000-8000-00805f9b34fb",
  "deviceID": "xxxxx-xxxx-xxxx-xxxx-xxxx",
  "isWritableWithoutResponse": false,
  [...]
}

The only property that looks like could be the answer is the value property, the value itself looks different.

How do I interpret the battery level from the response?

[simonbothen-radinn]

@ibrahim-delice The value is in base64. See https://github.com/dotintent/react-native-ble-plx/wiki/=--FAQ:-Passing-And-Retrieving-Of-Characteristic-Value for how to interpret it.

[ibrahim-delice]

Thank you but I managed to do it like this:

const batteryCharacteristic = await device.readCharacteristicForService(
      '0000180F-0000-1000-8000-00805f9b34fb',
      '00002a19-0000-1000-8000-00805f9b34fb',
    );

const currentBatteryLevel = Buffer.from(
      batteryCharacteristic && batteryCharacteristic.value
        ? batteryCharacteristic.value
        : '',
    ).readInt8();

[Chasty]

@ibrahim-delice I get this value Nw== and then want to use your method and this error arises.

RangeError: Trying to access beyond buffer length, js engine: hermes

any idea?

[Sikandarkhan]

I faced similar issue. Managed to solve from the documentation link . https://github.com/dotintent/react-native-ble-plx/wiki/=--FAQ:-Passing-And-Retrieving-Of-Characteristic-Value#reading-value-from-a-characteristic

hope you find this useful.