MacBook Air not holding charge with an white x on the battery!!!!

I just got a new MacBook Air today and it isn't wanting to hold a charge it shows a white x in the middle of the battery symbol in the top of the screen and when I unplug the charger cord from the port it instant shuts off my MacBook. I looked in the settings to see the battery life and it is showing my battery is a good battery and still at 100% so I'm confused on what to do. I am currently trying to do a software update on it to see if that fixes it but if it doesn't I don't know what to do next. Does anyone have any idea how to fix my issue or what to do if me updating the software won't work?