// Codes used
float voltage;
bool flash;
void setup() {
  // 3,7v battery input.
  pinMode(A1,INPUT),
  // Battery level indicator LEDs.
  // Only cathode LEDs is ground.
  pinMode(0,OUTPUT), // Red LED
  pinMode(1,OUTPUT), // Orange LED
  pinMode(3,OUTPUT), // Yellow LED
  pinMode(4,OUTPUT); // Green LED
}
void loop() {
  if(flash = !flash,
    voltage = analogRead(A1)/204.6,
    delay(5e2),
    digitalWrite(0,voltage>2.50),
    digitalWrite(1,voltage>3.60),
    digitalWrite(3,voltage>3.90),
    digitalWrite(4,voltage>4.20),
    delay(5e2),voltage<3.30)
      digitalWrite(0,false);
}