Update with battery missing

Greetings Community,

my MacBook Air says that its battery is missing indicated by the x in the battery symbol. I reset it as I thought it would probably fix it. Now I'm stuck on lion as I can't perform an update. When I want to, it says connect to the ac adapter, which it obviously is. Now my question, does anyone know how to bypass this, so I can update the macbook?

And I won't change the battery as I will buy a new laptop in a year for university.

I plan on using the Macbook as a media center plugged into my TV.

Thank you in advance.