how do i calculate the loss of nitrogen pressure when filling an accumulator from a compressed nitrogen cylinder with 3500 psi and 304 cubic feet capacity, the accumulator will start with o pressure and and holds 50 liters of gas @ 70 bar?

also i need to fill 24 of these cylinders each with 50L @ 70 bar, and i know i can cascade the cylinders so that a cylinder with less than the maxium 70 bar can start filling a cylinder from o and then when the pressure equalizes i can "top off" to the max. pressure with a new cylinder?

is there a formula to do this? am i asking to much? do i know how to spell? am i loosing my mind?

Thank You in advance