int sensor = A0;
int LED = 13;
int light;
unsigned int battery = 0;
unsigned int capacity = 50000;
unsigned int ticks = 0;
unsigned int wait = 100;
double percentage;

void setup() {
  // put your setup code here, to run once:
  pinMode(LED,OUTPUT);
  Serial.begin(9600);
}

void PrintBatteryPercentage() {
  Serial.print(ticks);
  Serial.print("ms,   charge at ");
  percentage = 100 * ((double)battery / (double)capacity);
  Serial.print(percentage);
  Serial.println("%");
}

void loop() {
  // put your main code here, to run repeatedly:
  light = analogRead(sensor);
  battery += light;
  ticks += wait;

  if (battery >= capacity) {
    battery = capacity;
    Serial.print(ticks);
    Serial.print("ms   ");
    Serial.println("FULLY CHARGED");
    ticks = 0;
    delay(20000);
  } else {
    PrintBatteryPercentage();
  }

  delay(wait);
}