If your dry box has a RH meter, replace the desiccant when the meter is above 50%. The problem is that you will need to replace the desiccant every now and then, especially when you open and close the box frequently.
Dry cabinet has an electronic dehumidifier that works on electricity, the humidity inside is controlled and regulated at a set point. Typically from 30-40% RH.
That's the difference between a dry box & dry cabinet.