Permanantly Plugged in MacBook Implications.

Guidelines for prolonging Li-ion battery life

Unlike NiCad batteries or NiMH batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a longer time, they should be brought to a charge level of around 40%. Never use the battery care functions some cellular phones provide for nickel based batteries. (This will deep cycle the batteries.)

Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. Keeping them in very hot cars can kill lithium-ion batteries.

Avoid running the battery through "deep discharge" cycles that is using it until it's fully depleted to 0 %.

Many authors suggest that freezing Li-ion batteries may be detrimental. However, most Li-ion battery electrolytes freeze at approximately -40°C. Household freezers rarely reach below -20°C. Published experiments demonstrate that freezing (even below -40°C) is unharmful if the battery is fully warmed to room temperature before use. More details are given in the book "Characteristics and Behavior of 1M LiPF6 1EC:1DMC Electrolyte at Low Temperatures" by L.M. Cristo, T. B. Atwater, U.S. Army Research, Fort Monmouth, NJ.

Buy Li-ion batteries only when needed. Look at the manufacturing date. That is when the ageing process begins.

When using a notebook computer running from fixed line power over extended periods, it is advisable to remove the battery and store it in a cool place.

However, many laptop manufacturers recommend against removing the battery from a laptop while it is plugged in, as this can damage a laptop designed to operate with the battery installed. Some manufacturers are also concerned about dust accumulation with the battery removed. Therefore, check the manufacturer's instructions before removing the battery.