Touchscreens *shudders* :3
But in reality you wouldn't even need it. If you have a tree farm big enough, with enough furnaces, to produce 1 stack of charcoal every <x> minutes (x=b*t, b=burn time of a stack of charcoal t=amount of turtles) then you just have the charcoal being produced at the same rate it is being burned, then no harm done. And if you have a set up like so:
CC
H
E
C being a chest, so in this case a double chest (use Iron chests if installed), H being a hopper, and E being the Enderchest....
Then have the turtles filling the chests, attempt to fill E then H then C, that way even if the ender chest is full then the charcoal is still being put into the system. And if the turtles manage to empty the ender chest of the full stacks, then there will still be a few that are starting to get put in, via the hopper, for any turtle which still needs some... although it won't be a stack, it would still be a small amount of fuel, enough to go on a little while longer