I have an iPhone 6. My battery drains quickly and has a battery health of 73% . I need a new battery. Are the replacement batteries for this phone still $29.00 and do I need to make a reservation at the store for replacement or walk in?

Battery price is still the same, since it is Apple you might want to get a reservation being that they are often packed

Making a reservation will make it easier for you. Walking in will only work if they aren't booked with reservations. Before going in I recommend cleaning out any apps that maybe running in the background and updating your phone. All iPhones seem to have the same problem with their battery when new software comes out

Yes, batteries are still the same price and no reservations needed.