Q: my phone's battery is discharging very rapidly even when not in use, what should i do to fix that?

Hello rabeeha hafeez robi,

Thank you for using Apple Support Communities. It's my understanding your iPhone battery has been draining more than expected. I use my iPhone everyday so I know how important battery life can be. I can surely understand your concern, especially since it seems to occur while the phone isn't in use.

First, I recommend checking your settings to see what is using your battery life. You can do this by going to Settings > Battery. In some cases an app's Background Activity can impact the battery life. This means the battery is being used by an app while it's in the background. The link below provides additional information and tips to help maximize your battery performance.
Batteries - Maximizing Performance

Cheers.

Thank you for following up. At this point it's possible this issue is being caused by the software or content. To help resolve software issues we recommend restoring the iPhone with iTunes. This allows iTunes to remove all content and reinstall the software. To protect your valuable information, it's important to back up first. Once you've successfully restored you can bring back all content by restoring from the backup. Use the links below to assist with backing up and restoring in iTunes.
 

How to back up your iPhone, iPad, and iPod touch

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings

Restore your iPhone, iPad, or iPod touch from a backup


Have a great day! 

We're glad to hear your iPhone is charging appropriately. Since you're still experiencing the issue with discharging we recommend contacting Apple Support for further assistance.
Contact Apple Support