Kakashi's been using his sharingan this whole war. His stamina have increased.
Kakashi without Sharingan = 5/5
Kakashi with Sharingan= 4 or 4.5/5
Kakashi with Mangekyo Sharingan = 2 or 3/5 Since Guy said he doesn't have enough strength to wrap away 4 Tailed Beast Bombs.
Also, Could being inside the Kyuubi Chakra cloak have recharged them?
what they display is chakra control using what chakra they have more efficiently than most, but in sheer reserves someone like itachi or kakashi really dont have an obscene amount of chakra, that said given observations about how long his sharingan has been active and how many raikiri's hes used either his chakra control has drastically gone up or his chakra reserves have mildly gone up, cant really say either or
It also states Kurenai is a 5 in Genjutsu, but Itachi easily made her look like a Genin.