Since installing Snow Leopard, a large number of MacBook and MacBook Pro owners have noticed a problem with the computer frequently displaying a "Service Battery" warning in the battery system menu. This also seems to be coupled with relatively short battery life, either with the battery discharging rapidly or with the computer going to sleep but still reporting high percentage of charge left in the battery. As of OS 10.6.2, affected users are still experiencing the problem.
This problem appears to be an issue with Snow Leopard's handling of the battery hardware, where the services that are supposed to detect battery problems are incorrectly reporting the battery status, and subsequently triggering the system to go into a precautionary sleep mode or claiming the battery is draining. This is especially supported by the fact that affected people who have downgraded back to Leopard either by reinstalling, restoring from backup, or even booting off the 10.5 Leopard DVD have not had the problem occur on the same hardware.
While a few people have had obvious hardware defects such as swelling batteries, others with normal batteries are having the same problem. A TUAW article on the problems suggests this behavior is from Snow Leopard being fine-tuned to reveal existing battery problems that Leopard was not aware of. While this may be the case for some people, the sheer number of people reporting the problem indicates there may be errors in the software. Unfortunately, there is no easy way to discern those with pre-existing battery problems from those with healthy batteries.
Despite this problem existing for a number of MacBook owners, overall most people using Snow Leopard have not been affected. In a reader poll by Gizmodo with over 4500 responses, most people have found the battery life to be about the same or maybe only a little worse as before upgrading, with reports of "magically better" battery life being roughly equal in number to those of "tragically bad" battery life.
Addressing the issue
Power and hardware problems always bring to mind the following suggestions as possible fixes; however, while performing these steps have shown some success for a few people, many others have not been able to overcome the problem. Despite this, they are worth a shot and may need to be performed multiple times in order to kick in properly.
Strangely, the battery issues have cleared for a few users who have just shut down and restarted their systems on a regular basis. While keeping the power supply plugged in to prevent any issued with the battery, they've turned off the machine and rebooted to see the battery being normally recognized. This suggests the problem may be with a setting more than a specific bug, that hopefully can be reset by a full restart. MacBook owners may tend to sleep their systems instead of restarting them, which will keep various settings from being refreshed.
Further supporting the claim of software issues in Snow Leopard is that some people have cleared the problem by booting into 64-bit mode. If you do not have any software that requires a 32-bit kernel and system extensions, try booting into 64-bit mode by restarting and holding down the "6" and "4" keys simultaneously. For some the problem has returned when booted back into 32-bit mode, but for others the switch to 64-bit mode has fixed it even when booted into 32-bit mode.
Another suggestion to address this problem is to remove the power management system preferences, which contains parameters that determine how the system will behave when running on either AC power, battery, or a UPS. This file is called "com.apple.PowerManagement.plist", is located in the /Macintosh HD/Library/Preferences/SystemConfiguration/ folder, and can be removed without harming anything; however, those who have done this have found it only seems to temporarily remove the warning in the battery system menu, and does not address the underlying issue.
Lastly, this problem may be with the upgrade process itself, where settings for Leopard are not working with Snow Leopard. The temporary successes with removal of the Power Management property list suggests this may be a possibility. As a result, try booting off a clean OS installation of Snow Leopard to test the hardware. This can be done by installing to a spare external hard drive (recommended), or by formatting and reinstalling Snow Leopard on your boot drive (be sure you have a full system backup before doing this). While booting off the Snow Leopard DVD is also an option, the installation on the DVD is a minimal one with only the services and programs needed to install the OS and diagnose problems, so it may not be a thorough way to test.
Proper Battery Care
There is great debate on what is best for maintaining a battery. While Apple has a few resources with information on how to calibrate and maintain the battery, numerous people have their own suggestions and philosophies for how to best use the battery, which range from frequent and heavy usage to regularly scheduled charges and calibrations.
Overall, the take-home message for how to maintain the battery is to frequently use it. Let the system run on the battery, and let it run on the full range (charged to nearly uncharged) and you will get the most out of your battery. Add a few calibrations here and there (monthly or bimonthly), and you should be good to go. Sticking with a schedule is not as important as just regularly using the system on the battery, and ensuring that every so often you run a battery calibration.
For some tips on how to make the most out of your battery, see this.