Function getBattery not found on iTracker RAK 8212

Something's very wrong if you're trying to use Serial3. What about:

var at;
console.log("Turning Cell on");
require("iTracker").setCellOn(true, function(usart) {
  console.log("Cell now on");
  at = require("AT").connect(usart);
  at.cmd("AT+CBC\r\n",1000,function cb(d) {
    if (d=="AT+CBC") return cb;
    if (d!="OK") console.log("CBC is "+d);
  });
});