I would want a 2, 3, even 7 day battery. Why not? I don't want to bother about charging every day.
But my worry is that with more and more efficiency in computing and battery tech, if Apple instead decides to reduce the battery capacity? Especially with no competition in sight, or competitors trying to follow Apple, we may end up with smaller batteries instead of more battery life. They seems to be doing that with iPhone. Also 18 hour battery life can quickly degrade to few hours if some processes are spinning the CPU continuously which can happen knowingly or unknowingly with several apps open (Docker occasionally does that to my MBP).
With several days battery life, I can even go for short travels without even bothering about how to charge it.
The problem with multi day battery life is you never get in to a routine and you get caught out every time. I had a pebble watch which had a 10 day battery life and almost every 10th day it would go flat on me mid day or I'd get a warning about low battery while I'm outside and then forget about it when I get home.
Now I have an Apple Watch that lasts almost but not quite 2 days, I charge it every night and it has never gone flat on me and I find it no hassle since I take it off before bed anyway so I just drop it on the charger.
Kindles suffer this problem. The battery lasts forever so you never get in the habit of charging them. Then you get caught out and it's at 0% and you can't read your book. Too much battery capacity is surprisingly harmful.
This is precisely why Kindles and similar devices should (a) use battery chemistries that are power dense so that they can charge quickly, and (b) come with a wireless charging mat that you can set up on an end table wherever you like to read (or where you put all your stuff when you walk in the door).
The only device that I don't have this issue with is my logitech mouse which gets 70 days on a single charge. It shows a red light on the side when its at about 2 days charge left and I usually remember to plug it in when I leave for lunch.
Especially now that thanks to USB-C, it's easier than ever to augment laptop batteries. For $60 you can grab a 100Wh RavPower battery pack that can double the lifespan of a MacBook.
But my worry is that with more and more efficiency in computing and battery tech, if Apple instead decides to reduce the battery capacity? Especially with no competition in sight, or competitors trying to follow Apple, we may end up with smaller batteries instead of more battery life. They seems to be doing that with iPhone. Also 18 hour battery life can quickly degrade to few hours if some processes are spinning the CPU continuously which can happen knowingly or unknowingly with several apps open (Docker occasionally does that to my MBP).
With several days battery life, I can even go for short travels without even bothering about how to charge it.