the number of cells along with the capacity of the cell is related to the battery life. commonly, people might have thought that, 'oh, this laptop has 4 cell, that has 3 cell, definitely the 4 cell will have longer lasting battery life!' but if you compare both of the laptops :

Dell Vostro 5470 - 3 Cell 50WHr
Dell Inspiron 14 - 4 Cell 40WHr

so the winner here is Vostro 5470, it can hold more capacity and last longer. and to add, yes, battery life varies between the processor and graphics card used.

yes.
they are calculated by capacity of cell x numbers of cell = MAh = convert to WHr