Not too long ago I borrowed a friend’s Hewlett Packard Pavilion N5190 notebook computer for a trip to Arizona. I figured that I’d finish writing a report and take in a movie of my choosing as the miles passed below. During the process of transferring a few files to my keychain hard drive and the notebook, I noticed that the battery was low and decided to recharge it. You can imagine my amazement when the battery was fully charged in 20 minutes and my shock when it was drained 8 minutes later.

Thinking that something was wrong with the battery, an HP F2193, I Googled it and found ample discussion in HP’s support forums, where it was revealed that the battery life is approximately 30 minutes on a good day and 5 minutes on a bad one. Thus, I needed to decide on buying a new battery pack or an adapter that could draw power from the airline. After six seconds of pensive thought, I decided to follow the prudent path and sleep during the flight.

The experience, of course, led me into all sorts of questions about notebook batteries and, never being one to shy away from such things, I plunged headlong into the electrifying depths of the notebook battery life.

NiCad (nickel cadmium) batteries are the oldsters of the industry and are nearly obsolete. Not in the 3-months old obsolete type of way, but the couple of years old kind of way. NiCd's have memory, which means that they work best when fully charged and should be run down fully; otherwise they won’t retain their full life.

NiMH (nickel metal-hydride) batteries don’t have a memory and can be recharged at any time. These batteries tend to have a peak life of 18 months.

Lit-Ion (lithium ion) batteries are the current state of the market and have the longest life of the three. They also weigh less than NiCad and NiMH batteries and have no memory.

For a variety of mystical reasons, notebook batteries are generally not interchangeable. Whereas every appliance that uses a double A battery can use those from Energizer to Rayovac, notebook owners are often denied the benefits from standardization and can be bound to use those from their notebook’s manufacturer.

Except in a few circumstances, such as the one tormenting me, most batteries will last between 1.5 and 3 hours. Runtimes vary based on the type of applications you are using. Applications that feature heavy graphics drain juice much quicker than MS Word. Similarly, if you’re powering an external device, such as a portable 80-gigabyte hard drive filled with 4,000 legally obtained MP3’s (cough cough), you can also expect a shorter runtime.

Folks that tend to use their notebook as if it were a desktop and leave it plugged in all the time are advised to remove their batteries. Leaving the battery installed will result in constant charging, which eventually reduces its life. The battery may also over-heat, which will cause the battery cells to slowly deteriorate over time.

One way to test if your battery is overheating is to run your computer with the battery installed and your notebook plugged in for a few hours. Then take two pieces of whole wheat bread, butter one side of each, sprinkle the buttered sides with parsley or basil and install two pieces of American cheese between them. Bring the two pieces of bread together and place one buttered side down on your desk. Place your notebook on top of the stack and wait for three minutes. If you hear a slight sizzling sound, have Granny put the kettle on because its time for lunch.

Of course, if your battery is hot enough to perform this test, I strongly advise that you not treat this notebook as a laptop computer. The good news is that if you do, you’ll probably only do so once. All joking aside, if you think your battery is running too hot, remove it and let it cool down. Then re-insert it and try again. If it still running at a temperature you believe is excessively hot, your battery may be defective and may need to be replaced.

Finally, when it is time to replace your batteries, don’t throw them out. The Rechargeable Battery Recycling Corporation (http://www.rbrc.com) can help you recycle your portable rechargeable batteries. You can find a drop off point near you by going to the site and many stores where you buy electronics participate in recycling programs.