According to many sources of information from the user community, the performance of the Macbook and its Pro-siblings may drop by 37% when running on battery-free AC power.
The charger does not always have enough power to power the machine and sometimes users have to use batteries to ensure stable power. Here, the problem we care about is how this specification will affect machine use. In testing with Cinebench R10 (multi-processor rendering test), the new 2.53 GHz Macbook Pro Unibody with 4 GB of RAM reached 5,549 points with battery and only 3,504 points if the battery was removed. This huge drop will have a significant impact on your daily work.
Do not remove the battery when using the Macbook Picture 2 Automatically disconnects when fully charged
Thus, the battery is always in the machine is essential to ensure maximum performance for the Macbook. Of course, you'll be worried about battery life, but Apple has anticipated this, Mac models have very good battery management capabilities and can automatically disconnect when fully charged, you can see this clearly. via System Information or battery icon on OS X's toolbar.
In addition, the device will only recharge the battery when the remaining capacity is below 95%, avoiding unnecessary charging will reduce the battery life. These two features allow users to place the battery in the slot and use the Macbook without having to worry about the life expectancy of other laptops.