Assuming we're talking about lithium ion chemistry, The most significant thing that will impact the longevity of the battery is heat, and keeping the battery at

Assuming we're talking about lithium ion chemistry, The most significant thing that will impact the longevity of the battery is heat, and keeping the battery at a high level of charge generates it. In particular, if you're always plugged in and the charging system is keeping it at 100%, this will impact the longevity in a meaningful way. Not sure about Macbooks, but my laptop has settings to control this. I typically have it setup to only start charging when the charge drops below 40% and to stop at 85%. Some other points: - It's preferable not to discharge fully. Very deep discharge can damage the battery, although all modern batteries have circuits to protect against this. - For long term storage, ~40% charge is best. That's why new phones typically come charged at around this level.