They won't. Call the store first before you even make a genius appt to see if they even have batteries. They won't. When I initially tried making a genius appt, with battery replacement option, all the dates a week out were unavail. I looked daily and saw a spot opened up. I assumed that this meant that a batter was avail. I went to discover they have no batteries, no idea when batteries would be coming in. Said probably not until end of Jan, when Apple initially said this $29 battery replacement would start. They did run a check and saw that the battery cycles were high and needed to be replaced. It was my sons iPhone6 and he would get text messages a couple hours later many times or a call would come in and the phone would ring but nothing was displayed.