In order to find out if they are eligible for the free battery replacement phone owners need to use Apple’s program page where they are provided with a way of checking their mobile phone’s serial number against Apple’s database. The serial number can be seen under the Settings->About.
Affected phone units can be delivered to any Apple Retail Store or to any Apple service provider. Additionally Apple fans that have a faulty unit can also make arrangements on the phone with Apple support technicians. This program launched yesterday in the United States and in China but will only be available in other countries starting with 29th August.
Apple will only provide this service free of charge until 1st of March 2015 or until 2 years passed since you purchased your unit (whichever date comes later so that it provides a longer coverage).