Laptops are ubiquitous, and cell phones even more so, but the vast majority of their owners know virtually nothing about how to properly care for the one element that makes these devices portable: their batteries. The peculiar characteristics of the lithium ion battery, as well as its expense, demand a little more care and attention than the common alkaline AA or 9 volt.
Identification
All laptops use lithium ion batteries, a battery design that generates electricity through the movement of lithium ions between the cathode and anode. Lithium ion batteries are rechargeable and offer one of the best power-to-weight ratios of any existing battery design.
Function
Most batteries of this design use graphite as the anode. The cathode is typically made from either lithium cobalt oxide, lithium iron phosphate or lithium manganese oxide. The choice of cathode is usually based on the balance between voltage, capacity and charge deterioration. Safety is also an issue, as some mishandled lithium ion battery designs have been known to explode. Electrical current is generated by the migration of the lithium ion from the anode to the cathode, and the reverse when it is being recharged. The electrolyte, or medium between the anode and cathode, is usually a solid lithium salt plus an organic solvent.
Considerations
One of the problems with a lithium ion battery is that, unlike other battery designs, it is prone to shelf decay whether it is used or not. While the design is rechargeable, from the time of manufacture a lithium ion battery gradually loses its capacity. The amount of charge it can hold steadily shrinks. If kept fully charged and at room temperature, a lithium ion battery will lose 1/4 of its capacity every year.
Warning
Another problem with lithium ion batteries is that keeping a high charge level will quicken the decay of the battery's capacity. Whenever you have your laptop hooked up to a power outlet recharging after it has already been recharged, you are essentially destroying the battery.
Prevention/Solution
There are two solid tips to follow with laptop batteries. First, try to avoid paying for an off-the-shelf battery. You have no idea how long it has been there, and therefore could be paying full price for a battery that has already lost a substantial portion of its capacity. Instead, buy directly from a manufacturer or wholesaler, a simple task in the age of Internet retail. Second, never leave your laptop plugged into the wall for no good purpose. It is, of course, a necessary convenience to recharge a laptop (or cell phone) battery overnight, but there is no need to leave it charging when it is already at full or nearly full charge during the day. If you are working and have your laptop hooked to a power outlet, either unplug the laptop or remove the battery.