You are mistaking. You don't make an appointment for a battery
replacement, you make an appointment for a battery
issue. There is no selection for battery replacement, but "battery service
request".
Additionally, if people would take the time to read, it clearly states there is low supply online and to CALL ahead to reserve one.
"Call Apple Support today to reserve a battery before visiting an Apple Store. Supplies of replacement batteries are currently limited for iPhone 6, iPhone 6 Plus, and iPhone 6s Plus."
View attachment 746069
Maybe people can learn to take responsibility and stop blaming everyone else.