score:4
We (my wife and I) flew from Heathrow to Auckland two weeks ago with two defibrillators in our hand luggage (one each) without any issues at all - we had to put them through x-ray in their own trays (both at Heathrow and at Hong Kong), but were never questioned as to what they were or why we were carrying them.
Having checked several airlines rules on this, all emergency AEDs currently purchaseable by the public fall within the battery limits - although you won't be able to fly with a spare battery or a battery that isn't inserted into the device.