Maybe what's actually needed here is an addition to manuals to include the possibility that the defib, stored in the bin over row X seats A & B, may emit a beeping sound to denote when its battery is low and in order to maintain operability, such battery should be changed at the earliest opportunity...
Such might've made the F/A think 'that's not a banger, that's the defib low on bettery, better tell the CCM so that it can be logged and the battery changed at ORD (or wherever)'. In the absence of which, hearing something unknown beeping apparently from an unknown box, they're free to draw other conclusions.
So no-one's fault, just something which might help in the future.