What is the burden of proving a search warrant was obtained without a warrant?

When a defendant moves to suppress evidence seized in a warrantless search, the prosecution bears the burden to prove police conducted the search under a valid exception to the Fourth Amendment's warrant requirement. (People v. Camacho (2000) 23 Cal.4th 824, 830.) "In reviewing a trial court's ruling on a motion to suppress evidence, we defer to that court's factual findings, express or implied, if they are supported by substantial evidence. [Citation.] We exercise our independent judgment in determining whether, on the facts presented, the search or seizure was reasonable under the Fourth Amendment." (People v. Lenart (2004) 32 Cal.4th 1107, 1119.)