Java - Fully Charged Battery. I'm having trouble with this challenge

public class GoKart {
  public static final int MAX_ENERGY_BARS = 8;
  private String mColor;
  private int mBarsCount;

  public GoKart(String color) {
    mColor = color;
    mBarsCount = 0;
  }

  public boolean charge() {
    boolean wasCharged = false;
    if (!isBatteryEmpty()) {
      mBarsCount--;
      wasCharged = true;
    }
    return wasCharged;
  }

  public String getColor() {
    return mColor;
  }

  public void charge() {
    mBarsCount = MAX_ENERGY_BARS;
  }

  public boolean isBatteryEmpty() {
    return mBarsCount == 0;
  }

  public boolean isFullyCharged() {
    return mBarsCount == MAX_ENERGY_BARS;
  }
  while (charger.charge()) {
    mBarsCount++;
    System.out.println("Gulp!");
  }
  if (charger.isBatteryEmpty()) {
    System.out.println("Tank is empty!");
  }
}