People are often confused about batteries, and understandably so because there are many different types of batteries and each has its own different characteristics.
It is not always easy to know what kind of battery you are dealing with, and to make matters worse, things keep changing such that the advice that was correct years ago is no longer applicable today.
A case in point is the rechargeable batteries used in laptop computers. Many years ago the best advice was to take your battery out of the computer if you wanted to conserve its lifespan. Today just the opposite is true and if you take the battery out of the computer this may hasten its demise. The reason for this is that laptop batteries have changed dramatically.
Batteries made with nickel–cadmium used to be the norm. Their best characteristic was the capability of lasting 500 to 1,000 full charge/discharge cycles without deteriorating past the point of usefulness. Nicad batteries are very quick to take a charge. Their problem was the “memory effect” resulting in severe loss of capacity if not treated properly. Nicad batteries should be completely discharged then charged.
Today laptops use batteries composed of lithium-ion. This chemical composition has no memory effect problems, and better energy density. Lith-ion batteries are slow to charge and should not be completely discharged. They are best kept fully charged without over-charging. For best results you should always plug your laptop into AC power whenever available to keep the battery topped up. Unplug the laptop from AC power when fully charged, this for safety reasons.
Safety? Lithium-ion batteries are flammable and there were significant safety concerns to be addressed before they could come into widespread use. Lith-ion batteries should never be overcharged and so the circuitry of your laptop prevents that from happening. Still, you can go on Youtube.com and find the video of a laptop bursting into flames. That is why I suggest unplugging your laptop when not in use.
You can see that the rules for laptop batteries changed quit a bit. Many years ago it was a good idea to use a laptop battery until it was completely drained, then charge it. Today just the opposite is true because draining the battery until it is completely dead is not good for it. By some estimates deep-cycling a modern lith-ion battery can reduce its usable life by half.
I recommend plugging your laptop into AC power to charge the battery at home, plug it in at work, charge it at the coffee shop, on the bus or plane; anywhere you have an AC power outlet conveniently available you should use it. Doing this gives your lith-ion battery the most longevity plus it means the battery will be charged when you do need to use it.
Just an aside, everything here applies equally to lithium-ion batteries used in cell phones.
Charles Miller is a freelance computer consultant with more than 20 years IT experience and a Texan with a lifetime love for Mexico. The opinions expressed are his own. He may be contacted through his web site at SMAguru.com.