I want them to be repeatably able in a crisis, not pegging out at a critical moment...
So do I ... but the only way to ensure that is to grab one* off the nearest Crash Cart!
Personally, I wouldn't place too much reliance on the one in the "remote village" (mountain top, wherever), train station or shopping centre. In fact, as hinted at before, myself I would ignore the thing altogether (or rather, leave it for someone else to have a go with) and make best efforts with
CPR.
*
Assuming they have been maintained as we would all have hoped.
