Early Boxsters are much worse than the NSX, killing a battery in a little over a week. I worked with a guy who traveled a lot, and if he left the car in the garage for over a week the battery was dead. The Porsche dealer said "that's they way it is" and sold him a Porsche-branded float charger (with about a $50 Porsche mark-up) to cure the problem. (The fact that Porsche had branded and stocked a float charger for that purpose kind of gives you a hint of how common a problem that was, and maybe still is in P-cars)
My NSX (bone stock electronics) will significantly drain the battery in 3 to 4 weeks, so I leave it on my $7 float charger in the winter. With that, my battery is now 11 years old and doing fine.
If your battery does get severely discharged & you want a chance the battery can be recovered, NEVER jump start the car or put it on a high current charge. Put it on a very very low current charge so that it takes 1 to 3 days to re-charge. That will let the battery plates re-form without overheating and warping the plates. Despite knowing that from design experience in the electronics industry, guess who forgot about that once and fried a new battery(not in the NSX)? I've also remembered that fact and tried it on a battery that was 3 years old and got many more years out of the battery.