Apple says your MacBook battery, when new, is good for about 4 ½ hours. Of course, there’s some variability, depending on what you’re doing with the computer. Here are a few tricks to keep your battery from dying on a long flight or something:

All laptop batteries eventually wear out, and as they do, they operate for less and less time. You can prolong the life of your battery with regular monthly maintenance. Once a month, run your MacBook on battery until it puts itself to sleep, indicating the battery is empty. Then plug it in and fully recharge it.
You’ll have to decide when to replace your MacBook battery. You can get an add-in utility to track your battery capacity, and replace the battery if you notice the capacity is dropping. Or you can just monitor how long your MacBook will run before going to sleep (keep track during your monthly maintenance). When the battery life falls below whatever your acceptable level is, it’s time for a new one.
Links to battery capacity apps:
Helpful links for more info:
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