Hello Pushkar08! Thank you for participating in the Apple Support Communities.
We understand that your battery is draining overnight, and you're not sure why. We'd like to look into this with you to see how we can help.
According to the screenshot, it looks like there's a high amount of usage between 12AM - 2AM. When you tap one of the columns on your screen, you can see which apps contributed to your battery usage during that time period, and the proportion of battery used for the app.
That may help narrow down what app is causing the battery drain. For more information, see here: About the battery usage on your iPhone, iPad, and iPod touch
Make it a great day!