Battery constructor

Battery()

Constructs a singleton instance of Battery.

Battery is designed to work as a singleton.

Implementation

// When a second instance is created, the first instance will not be able to listen to the
// EventChannel because it is overridden. Forcing the class to be a singleton class can prevent
// misuse of creating a second instance from a programmer.
factory Battery() {
  _singleton ??= Battery._();
  return _singleton!;
}