Did you mean to change it to a question, or to ask if the following is sensible?
I'd be better to get a quart.
If you said that to me I could respond by making a quizzical face and say:
"I'd be better to get a quart?"
(...as a challenge to the fact that I didn't understand what you just said, because it sounds weird.)
Yet it could pass for old-timey pirate language, as a sort of short-hand for "I'd be better off if I were to get a quart."
first mate: "Cap'N, would you like me fetch ye a gallon of skunk whiskey?"
cap'n: "Arrr, nay! I'd be better to get a quart of yonder Basil Hayden."
If you spoke like that people would know what you mean (and that you were a pirate). But it's not normal speech, and you should go with "I'd better get a quart."...assuming you live in a place where people know what quarts are.