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Based on the apple article 86284 calibrating your new lithium ion battery is the best way to maintain its health. While Apple suggests that you do this calibration, which essentially amounts to running your laptop on the battery from full charge all the way down to an empty charge, once every few months; I suggest doing this every day that you use the laptop. Based on the machines that we work on every day, it is possible to see a battery with a high energy capacity (mAh) and a high cycle count sometimes on the order of 400 - 500, while it is also possible to see an essentially dead battery with under 200 cycles. Based on our own experiments this seems to have a lot to due with the internal microprocessor that provides an estimate of the amount of energy in the battery as it charges and discharges and balances the capacity between each cell within the battery pack. In sort, using the battery is better than just keeping it attached to the system constantly without autonomous use. I don't advise taking the battery out at night but putting your machine to sleep when you leave and shutting it down on the weekends or when not in use for extended periods is better for the computer, the battery, and energy consumption. A handy way to keep track of your batteries heath is in System Profiler _ Power. There you can see charge capacity and cycle count among other power related information.

The idea of cycling the batteries applies to nickel-cadmium batteries which did suffer from charging "memory" due to crystal formation. The lithium-ion battery in your MacBook and most current laptops do not have this problem. The sole reason for doing such cycling is to recalibrate your MacBook's software to more accurately estimate the remaining power in your battery because it does have a lifespan and will eventually die.

While Jonathan's suggestion of cycling your MacBook's battery every day may maximize the number of batteries cycles, I'm not sure that this would necessarily maximize the life of the battery. If you were to do a full cycle of the battery every day as suggested you would get a 730 cycle count over those same two years. Most of the recommendations I've seen suggested leaving lithium-ion batteries plugged in all of the time and thus topped off until you need to rely upon battery power.

I do agree that you should not run your MacBook without the battery, if only to avoid the loss of current information should you lose power whether due by accidentally unplugging your MacBook or due to power failure.

mrreet2001 wrote:

D'Eyncourt wrote:

The idea of cycling the batteries applies to nickel-cadmium batteries which did suffer from charging "memory" due to crystal formation.

It has nothing to do with nicd memory ...
[snip]

Huh? My understanding of NiCad battery memory is that crystals would form in the charged part of those batteries, and as those crystals grew they would reduce the battery life because there was less of the chemicals availble to be charged. To minimize the crystal formation (because some formation couldn't be avoided) one should fully cycle NiCads as often as possible.

My experience has been my batteries maintain their health for about a year and then start to go downhill and are not much use after two years.

If batteries (Mac batteries) were $49, most people wouldn't mind replacing them every year, but the high cost of laptop batteries is right up there with ink cartridges, even our volume cost is ridiculously high. We offer batteries as a connivence to our customers but don't really make any money on them.   

I'm curious to see how the new 17" unibody internal batteries hold up over time. Hopefully, they live up to at least some of the hype.