Captain Q.
I acknowledge your thirst for information, and to further assist you I can offer an insight into the Minimum Equipment LIst (MEL's) that the pilot uses to determine the a/c serviceability legally.
MEL 25-64-2 ..... Installed ..... Required
1. First aid kit ........4 .......... 3
2. Physicians Kit ..... 1 ......... 0
3. Defibrillator ...... 1 ......... 0
From what you can see a minimum of three first aid kits are mandatory, however only one kit is required to have been unused, the other two can have been used and not be full.
Legally I also recall from my training in first aid that we were told that there has never been a legal precedence set to prosecute someone for not offering medical assistance, whether trained or untrained.
As a first aider you would have been trained to keep the vitals going of any patient until appropriate medical help arrives, and I would suggest that this would still be the case with or without a defibrillator.
Good luck in your quest.