IANAL and I have no idea about the "rules of evidence" in the US, and only slightly more about UK rules but IIRC in the UK all evidence gathered by the police in any given investigation has to be supplied to the defence whether that evidence is used in Court or not, and that would by definition include anything garnered from BWCs.
I think the legal profession would smell a rat long before anything came to Court if material potentially helpful to a defendant (or a complainant in the case of a complaint against the police) was mysteriously missing because of an unexplained defect in a BWC.
Evidence - tampering is hardly unknown (sadly) but tampering with video evidence might be very hard to conceal, even by simply denying its availability. (What? Both (all?) BWCs used during this arrest were faulty?) It would not be long before defence barristers were asking about serial numbers of BWCs used against their clients, along with the test / maintenance records on them. And insisting on questioning the person(s) responsible for doing the downloads and storing the material.
I would suggest that "faulty BWCs" could very easily rebound hard on anyone (or any organisation) trying that approach.
Biting the hand that feeds IT
