Apple is currently offering a $50 credit for some out-of-warranty iPhone battery replacements and is in the process of contacting eligible customers by email. Customers who were not contacted by email should contact Apple directly if they believe that they should be eligible under the terms for the $50 credit. A battery replacement from Apple can be requested at support.apple.com/iphone/repair/battery-power.
The iPhone Battery Health screen shows battery usage by apps, maximum battery capacity, and peak performance capability. This screen is available for iPhone 6 and later with iOS 11.3 or higher, and can be found under Settings > Battery > Battery Health.
A list of current Apple product repair programs can be found at www.apple.com/support/exchange_repair.