battery life - What is it that kills laptop batteries?

There are many superstitions on what you must never do lest your battery become worthless - and by worthless I mean hold about 16 - 24 seconds of charge. This has happened to every laptop I have ever owned, and I just got a new one, so please help me sort out fact from fiction. Here are some of the things I've heard:

• Do not keep your laptop fully charged. You must run it completely down every so often.


• Do not use your laptop plugged in to the wall. Only plug it in when it needs charge.


• If you will not be using your laptop for a long period of time, don't leave it at full charge.


• Do not leave your laptop running 24/7.

The first two I know to be complete fiction: this was true of old batteries such as you might have had in an iPod in 2003, but modern batteries function better when kept at or near full charge. Devices even have circuitry to prevent you from completely depleting your battery, as this is dangerous.

The third point sounds probable, and I'd be interested to know if it was true. However, it doesn't really apply to me because I'm not really the type to leave my laptop alone for a day, much less a "long period of time"

The fourth seems most likely of the above, but only because of causality: I have always done this, and my batteries have always crapped out on me. I've generally treated a laptop like a desktop with a battery backup, and that I can move from one room to another if necessary. The fact that my batteries tend to last less than 30 seconds has further entrenched this behavior. Should I be trying to break this habit?

Are there any other things that ruin laptop batteries? I love that I can actually use my new laptop unplugged :) I'd like to keep it that way.

Update: Additional question: If the computer will be used for an extended period of time plugged in, does it make sense to remove the battery first?

Update 2: I know people with laptops older than mine, who actively use their laptops as much as I do, and their batteries still hold about an hours' charge while mine holds less than 30 seconds, hence my belief that something I'm doing kills them.

Answer

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries has some useful information. It suggests the following tips regarding lithium-ion batteries:

1. Don't fully discharge the battery (partial discharges are best)


2. Don't heat up the battery when it's fully charged


3. Ideal storage is about half charged in a cool environment.

Tip 2 would support the idea of not using a laptop while fully charged and plugged in, as laptops generate significant heat, and 3 would suggest against leaving a laptop in a car that's in the sun.

In the end I would think it's just simple degradation that renders batteries useless. There's only about 500 charge cycles on a lithium-ion battery before it becomes next to useless. Sure this improves as the technology matures, but I don't believe anything radical has changed since the linked article was updated.