Am I damaging my battery by never using it?

Short answer: yes, this will damage your battery. Take it out for extended periods when it's not going to be used.

Lithium Ion batteries (as in your laptop) have a pretty short life anyway. Even if you leave it sitting on a shelf, never used, within 5 years or so it will be useless (which is why I feel sorry for people who are buying the $100,000 Telsa car, it's loaded with batteries that won't last for more than a few years!).

There's a great explanation of why this is on Wikipedia.

Factors affecting Li-Ion battery life:

• Everything I've read says that Li-Ion batteries last longest if they're kept cool and lightly cycled: run them down a little bit and then charge them.

• They basically have a fixed number of discharge/charge cycles, so keeping them plugged in most of the time is fine. I see 300-500 cycles mentioned frequently, one site has it as high as 1000. Since Li-Ion's don't have memory effects, you don't need to "waste" cycles by running them down.

• Li-Ion batteries are sensitive to temperature, so if the computer runs hot, you're better off taking the battery out when the computer is plugged in. Anything else you can do to keep the batteries cool is a good idea.

• All batteries self-discharge, but Li-Ion's are slower than NiCads or NiMH's. So if you leave your batteries out for a long time, they'll need to be charged up again.

At one point, I tried to preserve my battery by taking it out when I was just sitting in the office w/ my laptop plugged in, but then I gave up and figured that for the life of my notebook, I could probably count on the batteries being available to buy a new one after a couple of years so I just use it and hope for the best.

Good sites for battery info:

Battery University: The Li-Ion Battery

Power Electronics article on Li-Ion battery care

Battery Education: How many times can I charge my battery

Apple has a good webpage about batteries and an iCal calendar to remind you to regulary do a cycle.

Lithium-ion polymer batteries need to be used for maximum performance. If you don’t use your device often, be sure to complete a charge cycle at least once a month.

Supposedly, the new MacBook Pros have "adaptive charging" that is tuned to each individual battery cell. This is designed to eliminate the headaches associated with maintaining lithium batteries that used older charging technology.

The technology is also supposed to extend the number of recharge cycles. It accomplishes this by tuning the charging and discharging of each individual cell.

See here for the marketing material on the subject.

This is what I do, as it's been recommended by the manufacturer:

1. Unplug the computer when it's not on (so that it's not constantly trying to charge the battery).
2. Keep the battery in the computer when it's on, but plug the computer in (so that it maintains a full charge for when I need it, but it gets charged slower).

I've lost less than 5% of the battery's capacity over the past 9 months that I've had this laptop this way. My wife's laptop battery however, has been pretty much wiped out over the past 3 years.

If however, your computer is always at your desk and you never take it mobile, then it's probably best to remove the battery entirely because you don't use it. Drain the battery to between 40 and 60%, then put it in the refrigerator. It will permanently lose 2% of its capacity over the course of a year if you do it this way, versus 20% if you keep it fully charged at room temperature.

Lithium ion batteries can generally survive for 1000 or more cycles, and a partial cycle only counts as a partial cycle, unlike (much older!) NiCd or NIMH batteries, which can build a memory effect.

By the way, to respond to another poster, the Tesla manages its battery pack much differently from a laptop in order to extend its life. That pack is never charged to full capacity (I believe 80 or 85%) and never allowed to drain less than 20%. Laptop users are much more picky about discharge times, and their manufacturers much less worried about how many years the batteries last than they are about selling more laptops than the next guy. Also, the battery pack they're using in the production cars are of a different chemistry than their original prototype (which actually used laptop batteries), for safety.

I'm with Ward. My understanding of li-ion batteries is that they have a charge-cycle lifespan and that keeping them plugged in is the best way to preserve it's lifespan.

I think the official word from Apple is charge...drain...charge at least once a month or so to properly calibrate it... but then again Apple is known for making a buck or two off of dead batteries so I would take their advice with a few spoonfuls of salt.

If you are using your macbook on the adapter all the time, it was recommended to me by one of the apple genius' that you remove the battery.

I had my battery die (not charging and pulling the power killed the laptop) and they ran their battery diagnostics on it, it showed that it had completed 300 charge cycles. THis was explained to me as when you are using it on adapter, it will actually run on battery until about 95% then top up your battery and that increments your Charge Counter. If it's over a certain amount then they won't replace the battery in warranty.