Restarting the phone first can help solve some temporary problems. Secondly, make sure your iOS system is up to date, because the update may fix some known problems. Then, clear the battery history, which helps to reset the battery statistics. Next, check whether the battery is normal. You can check the status of the battery by going to Settings-Battery-Battery Health. If the above steps cannot cancel the unknown part of the battery, it is recommended to seek professional technical support. You can contact Apple customer support or send your phone to an authorized Apple service center for inspection and repair.