Mac users looking to get some insight into their battery power outside of the typical X% charge left should take a look at the freeware utility coconutBattery.
coconutBattery isn’t just a tool which shows you only the current charge of your battery – it also shows you the current maximum capacity of it in relation to the original capacity your battery had as it left the factory.
You also get information about the battery-loadcycles (how often did you fully load your battery), the current charger (coconutBattery even warns you if you plugged in a wrong charger for your Notebook) and last but not least information about the age of your Mac.
As with most all batteries, there is more to them than just the charge left. coconutBattery allows you to actually capture overall battery readings at specific times which you can use to easily compare to future readings. Having advanced information such as this can help you determine the overall health of your battery and even give you some indication of when the ‘end of life’ might be near.