Reader Karl Schwartz believes his laptop's battery is troubled enough that it needs analysis. He writes:
I have a 15" MacBook Pro and was wondering if there was a built-in diagnostic to analyze my battery.
There is. Launch System Profiler (found in the Utilities folder or by choosing About This Mac from the Apple menu and then clicking the More Info button), select Battery in the Contents pane, and Battery Information will be the first entry. If you're running Leopard, under the Health Information heading you'll see Cycle Count and Condition entries. If you're running Tiger, you won't see a Condition entry.
The Cycle Count entry gives you some idea of how far along in its life the battery is. According to Apple, "a properly maintained Apple notebook battery is designed to retain up to 80% of its original capacity at 300 full charge and discharge cycles." So, if you're nearing that 300 cycles, you understand that your battery is going to offer less of a charge the longer you use it.
The Condition entry should always read Good. If it reads anything other than Good, you could have a problem--the kind of thing you might want to discuss with Apple if you haven't had the laptop for long.
If you're running a version of OS X that doesn't tell you everything you want to know, glom onto a copy of Sonora Graphics' free Battery Health Monitor application. It provides stats on the battery's original and current capacities, current charge, charge cycles, and voltage in an easy-to-read interface.