This How to Prolong Lithium Based Batteries article from Battery U. is a nice summation of the tech and operating issues around modern laptop and mobile phone batteries, and gives some good tips on keeping your battery going longer.
All batteries are consumables of course, but there are things you can do to extend the life of your portable friend to its fullest. For one thing it’s clear that heat is the enemy, so keeping a battery as cool as possible helps a lot. I always keep my laptop elevated off the desktop with some small object for this very reason. Definitely worth a read.
Heat buildup is always a concern and running a laptop in bed or on a pillow may contribute to this by restricting airflow. Not only will heat stress electronic components, elevated temperature causes the electrodes in the battery to react with the electrolyte and this will permanently lower the capacity. Placing a ruler or other object under the laptop to increase floor clearance improves air circulation around the enclosure and keeps the unit cooler.