A good deal of the insulation batting in our crawlspace needs to be replaced. Some areas are completely bare. But the width between beams is about 44 inches, and I can't find any batting that's even close to that width. (The current insulation is that wide, but it's very old.) Any suggestions are appreciated. Thanks
A "bib system" is often used in these scenarios. A mesh is stapled to the underside of the joists, and fiberglass is blown into each cavity.
If you really want to use batts you'll need to support them somehow. You could install strips across the voids and lay the batts on them. You'll need to use several rows and cut to fit.