How to read battery level from Arduino while it is powered via 9v Battery barrel jack

I would like to know how to read battery level from Arduino while it is powered via 9v Battery barrel jack.

Thanks, Jyoti RAJ

Solution

With battery level you mean voltage. You can measure voltage using one of Arduinos analog inputs. As 9V would kill your Arduino you need a voltage divider which allows you to measure a safe voltage that is proportional to the battery voltage.