What is the burden of proving a defendant validly waived their Miranda right?

The People bear the burden of proving by a preponderance of the evidence that a defendant validly waived his or her Miranda rights. (Colorado v. Connelly (1986) 479 U.S. 157, 168; People v. Duren (1973) 9 Cal.3d 218, 237 (Duren).) "[T]he courts will not lightly find that there has been a waiver of a fundamental constitutional right, but, rather, will indulge in every reasonable presumption against a waiver." (Duren, at p. 237.)

On appeal, however, defendant bears the burden of establishing that he did not competently and intelligently waive the right. (Duren, supra, 9 Cal.3d at pp. 237-238.) " 'The question whether an accused waived his right to counsel and his right to remain silent before making a statement to police officers is primarily a question of fact for the trial judge.' " (Id. at p. 238,) " '[W]e accept the trial court's resolution of disputed facts and inferences, and its evaluation of credibility, if supported by substantial evidence. [Citation.] Although we independently determine whether, from the undisputed facts and those properly found by the trial court, the challenged statements were illegally obtained [citation], we " 'give great weight to the considered conclusions' of a lower court that has previously reviewed the same evidence." ' " (People v. Whitson, supra, 17 Cal.4th at p. 248.)