Case in point, a wedding 2 days: in the grip of my D800 on for 2x 6h I still do not have the indicator "in a short time, this is the battery of the device will take over" .
Nikon SB900> over 700 flash (ttl in places really not very enlightened) before they are discharged.
So yes, they are not given, but since he really must want to unload, frankly it's worth the shot;)