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.