I charge mine every night. Sometimes it’s down to <50%, others at about 80% but I use it as an alarm clock and it’s convenient to plug it in and leave it on the bedside table.
Yes. More advanced battery metering involves some dedicates circuits that monitor how many happy little electrons go in and out of the battery during charge and discharge cycles. It has a pretty good idea of how the phone tends to behave, but can be tweaked for your specific phone and battery, to deal with tolerances.
I’m not sure off hand how long it takes for it to learn, or if it’s really necessary to discharge all the way for the user to get benefits. But the underlying statements are accurate.
-D/a
That was all I could come up with myself, so thank you for telling me that. It’s the only thing tha made sense. 
That was…almost too much information to be useful to me,<hey, I flunked Electricity class in 7th grade> but I am having fun browsing through this. Thank you. 
The red zone is for charging and recharging only.
This is actually a factual question. Unless they’re deep cycle batteries, they should be charged as much as possible and drained as little as possible.
Personally, I have a charger at work, one in the car and several at home. I charge it all day at work, usually overnight too, and on road trips longer than about half an hour.
As has been mentioned, when talking about lithium batteries, that advice is wrong. A lithium-chemistry battery will have a longer life expectancy if it’s NOT constantly kept at a 100% charge. The optimum range for longevity is around 40% charge, but since that’s not practical, it’s best to charge it up as much as you need to, but then take it off the charger and use up that charge until it gets below ~40%, then recharge it as much as you need.
If, as you suggest, you charge it as much as possible, and leave it on the charger all the time so that it spends the majority of its time at 100% charge, it will have a lower life expectancy than if you just charged it, unplugged it, then started using up the charge. The more time it spends near the 40% charge range, and the less time it spends at the 100% charge range, the longer it will last.
There’s not much point in obsessing on it or anything, but it’s actually kind of nice to know that you shouldn’t be shy about using a wide range of the charge. It’s one of those rare cases where best-practice is actually more convenient and requires less fastidiousness - just charge it as much as you need, and use it as much as you want, and you’ll be doing fine.
I guess I should also mention a side-issue with leaving it plugged in and charging all the time, and that’s if you’re in the habit of also using the phone while it’s charging. Charging the battery generates heat, and using the phone (radios, display, & processor) generates heat, and if you’re also in a hot car while charging and using it, that’s even more external heat. HEAT = BAD for battery life expectancy. If possible, you should really avoid using the phone for extended periods of time while it’s charging. Just unplug it, use it, then plug it back in when you’re done, if you have enough battery capacity to do so.
Another consideration is whether your battery is removable or not. If the battery was not removable I would be a lot more careful about keeping it charged. Otherwise replacement batteries aren’t usually expensive. iPhone users, take care of your batteries, they aren’t (easily?) replaceable.
Thanks again for the input! I am no longer leaving it connected when I’m not using it. Of course it’s easier now that I have a new battery and it’s not going dead after 10 minutes. 