For information on how many hours a particular MacBook model can work without being connected to a power source, it’s best to refer to the user manual for your particular device. For the models released within the last two or three years, this time is approximately the same:
In MacBook Air (released 2018, 2019), the battery is supposed to last 12 hours of using a wireless connection, and up to 13 hours of continuous video playback on Apple TV.
The 13-inch MacBook Pro (released 2018, 2019) can run for up to 10 hours with a wireless connection and also play videos on Apple TV for up to 10 hours.
The 15-inch MacBook Pro (released 2018, 2019) has the same battery performance—up to 10 hours of keeping a charge.
For the 16-inch MacBook Pro (released 2019), the battery life provides for 11 hours of using a wireless connection, or up to 11 hours of video playback on Apple TV.
However, you have to remember that all these indicators are still only approximate numbers. The battery may drain faster due to the user’s intensive work in several resource-heavy applications at the same time, the background running of many programs, and other factors. Or it may last longer than the stated number of hours—for example, when a MacBook is simply switched on without any activity and with a minimum of processes running in the background.