In a hospital setting it is best to test defibs one at a time (one a day, for instance) ... else if you're not careful you (or rather, the patients) may be left vulnerable whilst they (the defibs) recover from their ordeal!

Ordeal? Yes. Bearing in mind that crash-cart defibs are generally regularly checked by user staff anyway, I always reckoned that biomeds need to test defibs under "realistic" (worst case) conditions:-
1) Unplug from the mains
2) Crank 'em up to max Joules
3) Carry out ten consecutive charges and discharges (into a tester) at max output
4) Note first and last output readings
5) Do a couple more discharges at different (lower) settings
6) Check that those (lower) outputs are within limits
If they pass that test (and they should), then they are good defibs! Otherwise, they are "false insurance". This is life-saving kit; but it's not much use if they whimper out after a couple of goes when someone has collapsed out in the car-park.

If they fail the test, the problem is (of course) most likely to be a useless battery (and yes, I have come across a few in my time - once there was a defib that couldn't even manage the
first charge to max - and that was "in use" at a North London hospital).

Then plug the thing back into the mains to re-charge the batteries. And leave it plugged in!
"Belts and braces", perhaps - but I always preferred to test defibs back at the workshop; for three reasons:-
1) To make sure the batteries were (good and) completely re-charged before taking it back
2) So as not to alarm the patients and staff!
3) When "out on the ward(s)" defibs always need to be ready for immediate use
