Battery Time Remaining Click to see a larger image

On a notebook Mac, there is a battery indicator in the Menu Bar with the other status icons on the left. You can click on the battery indicator to see an estimate of how much charge you have remaining on your battery.

Here are the different battery icon states and what they mean:

• You are running on battery power. The filled space of the battery gives you a rough idea of how much time you have remaining on the charge. The filled area will turn red when you have very little battery power left.
• Your battery is charging. If you click on the battery indicator icon when the battery is charging you will get an estimate of how much longer the batter needs to charge to get to full.
• Your battery is fully charged.

If you are more concrete than visual, click on the battery icon and choose Show. You will see options to show either the percentage or remaining time (estimated).

Most Mac notebooks also have a button either on the left side of the case or on the battery on the bottom of the computer that you can push to see how much battery charge is remaining. You can do this even while the Mac is asleep.

On a related thought: Batteries don't last forever. Here's how you can check the health of your notebook Mac battery:

1. Go to the Apple Menu and choosing About This Mac. When the About window opens, click the More Info… button. This will open the System Profiler.
2. Look down the list on the left and choose Power.
3. Under Health Information, look at Cycle count. For a recent notebook Mac without a removable battery, the battery should be good for around 1000 cycles. For and older notebook with a removable battery you should expect around 300 cycles. (This doesn't look like much of a difference until you figure in that a recent notebook Mac gets around 8-10 hours per cycle and and older notebook Mac gets around 4 hours.) More information on battery cycles can be found here.
4. Also under Health Information, look at the Condition. It will be Good, Normal, or Check Battery.