Laptop battery care
Making the most of your battery
Apple's advice is here: http://www.apple.com/batteries/notebooks.html
Keeping a battery under charge all the time is not a good idea. Best battery life is achieved with complete charge and discharge/use cycles. If you do not regularly need to use it on battery power, not plugged in, then set yourself a monthly reminder to discharge and recharge the battery.
Three to five years is a normal battery life for a Mac, but leaving a laptop plugged in 24/7 will cause the battery to die prematurely.
Coconut Battery (MacUpdate page) is a long-standing popular free utility which gives additional info on your battery.
iStat Pro (MacUpdate page) is a dashboard widget which displays data on battery usage, as well as system info such as processes that are running. It is not fully compatible with OS X 10.8 "Mountain Lion", but see this thread on MacRumors.com for a fix.
Apple recommends recalibrating your battery occasionally. While it will not extend your battery life, it will give you a more accurate picture of the true condition of your battery.
When you get a new laptop, it takes 5–10 cycles before your battery reaches a stable "original" capacity. So let it go through 10 cycles, then calibrate the battery, before taking a baseline, "original" reading. If you want an accurate reading two years down the road, recalibrate it first.
To recalibrate you have to run the battery down to nothing, then leave the computer unplugged for several more hours before plugging it into the mains and restarting it.
To see what difference it made, check the "Power" under both System Profiler and Coconut Battery before recalibrating, and then compare them to the results afterwards.
"Service Battery" warning
When your Mac laptop displays "Service Battery" in the Battery menu, it will not hold a charge for as long as it used to. If you need to use the computer where you do not have access to an electrical outlet, then see about changing your battery soon.
The time on battery will get shorter and shorter, but its final death is hard to predict. It may fall to under an hour within a few weeks, or even if you spin it out for some time, it may collapse quickly over days. If you are trying to get the last ounce of life from your battery, keep following the above advice about sometimes using the computer on battery only, to discharge it in cycles.
If you do not need to use it on battery power, then you can carry on using it plugged into the power socket. Modern batteries are better than the old alkali ones, and the risk to the other components (such as leakage) is low. Nevertheless there is a small possibility of damage e.g. to the power system. You may also have to put up with inconvenience such as re-setting the system clock after you switch on.
Make sure you order the right battery. It's wise to open the case so that you know what your battery looks like, or its part number.
If you live near an Apple Store, check whether they give you a lower price if you hand in your old battery.
iFixit.com gives instructions on changing the battery yourself.
- Lithium-ion Batteries, Apple's main page on the subject
Compiled by Neville Reid from a conversation on the Mac-Ministry List in January 2013, with advice on recalibrating from Aaron Hunyady and Marvin Robertson in 2010–11.