In the past, leaving devices always plugged in meant that I would end up with swollen batteries (with original iPhone it cracked the screen, with the Macbook it caused the trackpad to stop working). I replaced the Macbook battery and created a system where everything is unplugged for a while (a few hours, or a day) each week. No more swollen batteries.
A.
What's wrong with swollen batteries??? It just makes more room for reserve power.
My iPhone 5 battery swelled to the point of pushing the screen off. It had gotten to the point where I was having to charge it every 15 to 30 minutes of use.
The service center attempted to test the battery condition when I brought the phone in (still running on battery power). They said they had never seen a battery fail with such a low score on the test. I set a new record. Lol.
Installed a new battery, and it now takes a lot to run it down. I spend hours on it everyday and it never drops below 50% throughout my typical 20 hour day. Yes, I rarely sleep.
I got up this morning at 6 am, I used the phone to check emails, respond, and check package tracking info, browse the forums, reply, perform calculations on some papers.
Research things I'm working on.
By 11:30 I was sitting in a service center until 3 pm. Where I killed time on cellular data browsing and searching the Internet for information on several topics for numerous projects I got going on.
3:30 I get done at the service center (feeling annoyed at the long wait), and go about my day.
Spent about an hour talking on the phone. And then didn't do much with it after that except occasionally respond to emails.
Now it's past midnight, and I've been on the forums for about an hour.
Still not dead yet. Lol.
Over 50% left.
I charge it when I sleep. Which likely won't be for a few more hours.
I've treated laptops similarly as described by the other poster.... I leave them plugged in, until I need them to be portable. I've used all of the ones I've had like that. And they've always still delivered 3 to 4 hours of battery time per charge, even the ones that were 4 years old.