Americans almost always shorten the "had" in "had better" to just a "d" sound, using contractions like "you'd better," "I'd better," "we'd better." The "had" is still there, but it's harder to hear. In natural speech, Americans pretty much never say "had better" (it's the same as using "didn't," "isn't," and "can't" instead of "did not," "is not," "cannot").
A lot of Americans do also shorten the phrase to simply the word "better." You're right about the meaning. But the correct form is "had better," and in many cases, the "had" is just shortened in speech, so you might not hear it.