/// <summary>
 /// Add a method to call to the handler if the battery dies.
 /// </summary>
 /// <param name="handler"></param>
 public void RegisterHandler(BatteryIsDead handler)
 {
     batteryDeadHandler += handler;
 }
 public void DeregisterHandler(BatteryIsDead handler)
 {
     batteryDeadHandler -= handler;
 }
 public BatteryDeadObserver(BatteryIsDead handler)
 {
     batteryDeadHandler += handler;
 }