My personal Gmail account also sends and receives mail through my work address, same set-up as this guy. When composing a NEW email, the default "From" address is my personal account. Is there any way to change the default to my business account?
Goto your mail settings, accounts and import and you see "Send mail as:" from all your eligible mail accounts. Click the "Make default" link next to your desired id.
If you don't see your preferred mail id then please follow this link