The chip on the ink cartridge will show empty even after the tank has been refilled. To restore the chip setting to full it must be reset with an electronic chip resetter.
It is possible to use the refilled tank on the printer even though the chip indicates empty. However, you must always ensure that the cartridge has ink in it while printing. If it does not have ink while printing, permanent damage to the printhead will likely occur.
A reset chip allows the cartridge to electronically function as a new one. It will estimate the remaining ink in the tanks during printing and warn you when it is low.