!636 (modern)

main {
  static boolean kevinOn = true;
  
  psvm {
    int b = getBattery();
    say(b + " percent");
    int last = b;
    print("I'll be monitoring the battery every 10 seconds.");
    while (true) {
      sleep(10000);
      b = getBattery();
      if (b/5 != last/5) {
        say(b + " percent");
        last = b;
        print("I'll keep checking the battery every 10 seconds...");
      }
    }
  }

  static void say(String s) {
    print(s);
    if (kevinOn)
      try { kevin(s); } catch (Throwable e) { e.printStackTrace(); }
  }
}