Why does my MacBook Air quit several times a day?
Why does my my MacBook Air shut down several times a day?
MacBook Air, OS X Yosemite (10.10.5)
Are any messages associated with the shutdown? In other words, does it just spontaneously shut down, or are you prompted to restart your Mac?
If it suddenly shuts down on its own please read Reset the System Management Controller (SMC) on your Mac - Apple Support.
To potentially determine the reason for the shutdown (which may or may not ultimately help you solve it):
Wait until the Mac shuts down unexpectedly, then examine your system.log file to identify the numeric code associated with the shutdown. Read below.
Find the Console app - it is in your Utilities folder and looks like this
You can find it by selecting Utilities from the Finder's Go menu.
Open Console.
If the log list column on the left is not already displayed, show the log list by selecting Show Log List from Console's View menu.
Locate system.log in the list and select it. Many date and time-stamped entries will appear, hundreds of them, and you must find the entries relevant to your Mac's problem.
To do that type the words shutdown cause in the Filter field at the upper right of the Console window.
That will cause all log entries to be hidden, except for the entries containing those words. There will be a numeric code associated with the log entry starting with "Previous shutdown cause". What is that code?