You can see the charging level of the battery from the color of the LED display on top of the battery:

Green |  100 % – 71 %

Yellow  | 70 % – 41 %

Orange | 40 % – 16 %

Red | 15 % – 6 %

Red blinking | 5 % – 0 %

You can also find the charging level in de Pendix app.