Check Engine Light and Battery on 2007 Saturn Sky Red Line

I have a bad battery and now my check engine light is on. The dealer/mechanic states something may be draining the battery. What can be draining the battery to cause the engine light to come on?

Asked by for the 2007 Saturn Sky Red Line
You can have a battery drain caused by anything electrical that simulates a drain like leaving lights on. Can happen at any time. The cel may or may not be related. You can have two different problens. The cel will reveal codes to help diagnose.
Like the bike....anyway. I'm a woman so I have no clue? Do you think this is serious - or a quick fix? I am moving out of state on Thursday..the mechanic told me he would be hooking it up to a scanner in the morning..quick fix? serious or probably not?

Do you think it is serious?
Can only decide after see what codes are displayed when attach scanner.
OK. Thats what they told me...thanks much