Lothsahn, you are muddying the waters here.
Defective cell(s) are not a battery capacity warranty issue, they are a battery DEFECT warranty issue.
Nissan's protocols identify bad cells using what they call a CVLI test. See http://www.mynissanleaf.com/viewtopic.p ... li#p308501
Assuming the problem is defective cells (which is an assumption, because the cause is not known) then it would be a cell defect warranty issue. My point is that the warranty for battery defects does NOT state anything about a CVLI test. That is Nissan's protocol, yes, but not in the terms of the warranty. Proving the car's battery cells are defective is sufficient to trigger a warranty repair.
If their CVLI test did not show a problem, I'd tell them I still expect my car to be repaired, and if the problem is defective cells, it better be covered under the terms of the warranty. If the problem was NOT an issue of defective battery cells, then the owner is likely on the hook for the repair costs given the 77k miles, since all other systems run out at 60k miles.
I would not pursue the "safety" song and dance routine. All cars suffer a sudden loss of power when they run out of fuel.
Sudden, unexpected loss of power is absolutely a "safety" issue. ICE cars have been recalled for such. If the car reads teens of miles of fuel and then suddenly no fuel, that's a safety issue. If it simply had degraded range but proper indication, it would not be a safety issue.
A Leafspy report at LBW would be very good to see. Agree with the poster who said to NEVER charge above 80% to try to exacerbate the problem and trigger a failure of the CVLI test.