code: func NewBatteryService() *ble.Service {
  	lv := byte(100)
  	s := ble.NewService(ble.UUID16(0x180F))
  	c := s.NewCharacteristic(ble.UUID16(0x2A19))
  	c.HandleRead(
  		ble.ReadHandlerFunc(func(req ble.Request, rsp ble.ResponseWriter) {
  			rsp.Write([]byte{lv})
  			lv--
  		}))
  
  	// Characteristic User Description
  	c.NewDescriptor(ble.UUID16(0x2901)).SetValue([]byte("Battery level between 0 and 100 percent"))
  
  	// Characteristic Presentation Format
  	c.NewDescriptor(ble.UUID16(0x2904)).SetValue([]byte{4, 1, 39, 173, 1, 0, 0})
  
  	return s
  }
docs: // NewBatteryService ...