Bluetooth not work when using battery

I have a code is working before but since the code is using Serial1.onData when i upload my code is get warning so i change the code above.

the older code

function onInit() { Serial1.setup(9600);}
var trace = "";
Serial1.onData(function (e) {
  print("--->"+e.data);
  trace = +e.data;

if(trace  == "1" ){
  digitalWrite(LED3,1);
}
if(trace == "0" ){
 digitalWrite(LED3,0);
}

});
save();