Glad the steps worked on 2 - of course they should work on all three - something odd there. Has the odd one been soldered to?
You could use a version of the code above with all Serial removed since it will never help on a battery only situation. If that doesn't work to blink on all 3 you need to follow up with other troubleshooting specs or remedies - checking voltages etc.
Code:
#define qBlink() (digitalWriteFast(LED_BUILTIN, !digitalReadFast(LED_BUILTIN) )) // Pin13 on T3.x & LC
void setup() {
pinMode(LED_BUILTIN, OUTPUT);
digitalWrite(LED_BUILTIN, HIGH);
qBlink();
delay(200);
}
elapsedMillis emilBlink;
void loop() {
if ( emilBlink > 1000 ) {
qBlink();
emilBlink = 0;
}
}