I know it's pronounced "bet-tuh" which is how I pronounce it in my head... but when I talk, I say "bay-tuh" as that's what it's ALWAYS called around here. I've never, ever heard someone say it differently. To me, it's just another word that can be said multiple ways, like po-tay-to, po-tah-to. Getting mad about the "wrong" pronunciation won't change the fact that almost everyone says it "wrong".
But spelling it wrong is inexcusable xDD