演示效果：

这里是Github代码地址

实现步骤：

1.绘制电池边框
2.绘制当前矩形电量
3.显示电量文字
4.电量连续增长动效

实现代码：BatteryView类

/**
 * create by libo
 * create on 2020/7/22
 * description
 */
public class BatteryView extends View {
    private Path path;
    /**
     * 边框绘制paint
     */
    private Paint borderPaint;
    /**
     * 电量矩形
     */
    private Paint batteryPaint;
    /** 显示电量值 */
    private Paint textPain;
    private float powerLevel;
    private int width, height;
    /** 电池边框宽度 */
    private int strokeWidth = 12;


    public BatteryView(Context context) {
        super(context);
        init();
    }

    public BatteryView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        path = new Path();
        borderPaint = new Paint();
        borderPaint.setColor(getResources().getColor(R.color.white));
        borderPaint.setAntiAlias(true);
        borderPaint.setStrokeWidth(strokeWidth);
        borderPaint.setStyle(Paint.Style.STROKE);

        batteryPaint = new Paint();
        batteryPaint.setColor(getResources().getColor(R.color.red));

        textPain = new Paint();
        textPain.setColor(getResources().getColor(R.color.white));
        textPain.setTextSize(45);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        width = getMeasuredWidth();
        height = getMeasuredHeight();
    }

    /**
     * 设置电量类型
     */
    public void setPowerLevel(int powerLevel) {
        if (powerLevel == 10) {  //低电量
            batteryPaint.setColor(getResources().getColor(R.color.red));
        } else if (powerLevel == 40) {  //中电量
            batteryPaint.setColor(getResources().getColor(R.color.yellow));
        } else if (powerLevel == 80) {  //高电量
            batteryPaint.setColor(getResources().getColor(R.color.green));
        }

        this.powerLevel = powerLevel;

        invalidate();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        //绘制电池边框，使用Path来做，从左上角逆时针将电池边框画完成
        drawBorder(canvas);

        //绘制当前矩形电量
        drawPower(canvas);

        //显示电量文字显示
        drawPowerText(canvas);
    }

    private void drawBorder(Canvas canvas) {
        int headHeight = dp2px(getContext(), 30);
        int headWidth = dp2px(getContext(), 60);
        int sideLength = (width - headWidth)/2;
        path.moveTo(0, headHeight);
        path.lineTo(0, height);
        path.lineTo(width, height);
        path.lineTo(width, headHeight);
        path.lineTo(sideLength+headWidth, headHeight);
        path.lineTo(sideLength+headWidth, 0);
        path.lineTo(sideLength, 0);
        path.lineTo(sideLength, headHeight);
        path.lineTo(0, headHeight);
        canvas.drawPath(path, borderPaint);
    }

    private void drawPower(Canvas canvas) {
        Rect rect = new Rect(strokeWidth, (int) (height*(1-powerLevel/100*0.9)), width-strokeWidth, height-strokeWidth);
        canvas.drawRect(rect, batteryPaint);
    }

    private void drawPowerText(Canvas canvas) {
        Rect rect = new Rect();
        String text = powerLevel + "%";
        textPain.getTextBounds(text, 0, text.length(), rect);
        canvas.drawText(text, (width-rect.width())/2, height/2, textPain);
    }

    public static int dp2px(Context context, int dp) {
        return (int) (dp * context.getResources().getDisplayMetrics().density);
    }
}

MainActivity代码让电量持续增长：

public class MainActivity extends AppCompatActivity {
    private BatteryView batteryView;
    /** 电量值，用0-100表示 */
    private int powerLevel;

    private Handler handler = new Handler() {
        @Override
        public void handleMessage(@NonNull Message msg) {
            if (powerLevel > 100) {
                handler.removeMessages(0);
            } else {
                batteryView.setPowerLevel(powerLevel);
                powerLevel++;

                handler.sendEmptyMessageDelayed(0, 30);
            }

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        batteryView = findViewById(R.id.batteryview);

        handler.sendEmptyMessageDelayed(0, 100);
    }
}

打完收工。