The new feature was introduced in beta six; however, it takes a few weeks to finish.
In a thread on reddit, user StephIschoZen said their battery's maximum capacity went up from 88% to 94%. Other users reported the same. Logic33011's percentage increased from 85% to 87%u, user haenrqz said their percentage went up from 90% to 96%, and rafaqueque's went from 84% to 89%. However, there were reports of opposite. Andrew2511 said his percentage went down from 89% to 88% and user juniorspank's said theirs went from 90% to 87%.
Here's how Apple describes the recalibration feature.
iOS 14.5, coming later this spring, 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.
Apple is expected to release iOS 14.5 to the public following its special event on April 20th. Please download the iClarified app or follow iClarified on Twitter, Facebook, YouTube, and RSS for updates.