for me, a "beater" guitar should still play and sound ok. all my guitars (an '82 Gibson V, an Ibanez full hollow and a '78 Yamaha acoustic) are beaters. I don't treat them like a museum piece but I make sure they are 100% functional.
I have 2 or 3 dead guitars in my closet (80's Yamaha sg, 70's fender strat copy, no name cheap acoustic). eto yung talagang sira na and di na magagamit. I guess I can call them dead-beat guitars?