What will be the cost of changing iPhone 7 battery?

The cost of iPhone battery replacement can vary depending on the country or region you reside in. A few factors contribute to this price for replacing your iPhone's battery.

Apple Inc can replace your iPhone battery for a service fee. Their warranty doesn't cover batteries that wear down from normal use. 

iPhone Battery Repair & Replacement

Approx $69

iPhone Battery Repair & Replacement - Apple Support

Within the links these fine gentlemen provided, please use the “Get an Estimate” tool to determine an estimate for the cost of replacing the battery.