Hi there sufiyan786,
Thanks for joining us in Apple Support Communities! We understand the battery charge percentage on your iPhone 11 is fluctuating unexpectedly. We're glad you're here, and we can help.
To start, you'll want to be sure you've updated your iPhone to the latest software version, which is iOS 14.5. If needed, learn more about updating your iPhone here:
Update your iPhone, iPad, or iPod touch
After your iPhone is updated to iOS 14.5, you can go to Settings > Battery > Battery Health to see if any alerts appear there indicating battery health is being recalibrated.
"iOS 14.5 includes an update where the battery health reporting system will recalibrate maximum battery capacity* and peak performance capability on iPhone 11, iPhone 11 Pro, and iPhone 11 Pro Max to address inaccurate estimates of battery health reporting for some users. Symptoms of this bug include unexpected battery drain behavior or, in a small number of instances, reduced peak performance capability. This inaccurate battery health reporting does not reflect an issue with actual battery health." Have a look at this support article to learn more:
About recalibration of battery health reporting in iOS 14.5
We hope this information is helpful. Don’t hesitate to let us know if you have any more questions.
Cheers.