Where the battery lives depends on the Porsche. On the 911, Boxster, Cayman and 718 it is in the front luggage compartment under a plastic cover. On the Macan it is under the luggage floor at the back. Earlier Cayenne generations carry it under the driver's seat, which makes for a longer job. Most cars use an AGM battery. Some recent models leave the factory with a 12V lithium starter battery, which cannot simply be swapped for a lead-acid one.
Porsche's energy management tracks the battery's age and capacity. A new battery has to be registered with a diagnostic tool, otherwise the car keeps charging it like the old one and can go on showing a battery warning. A memory saver protects the settings during the change. Porsches driven only at weekends lose charge while parked, and a flat battery can leave the front lid locked. On the 911 and 718 an emergency terminal in the fuse box deals with exactly that.