When you refill an HP cartridge the chances are that when you put it into your printer it will report as empty.  This is because the printer remembers the cartridge and refuses to reset the ink meter.  Don’t worry, the meter is only an estimate.  Go ahead and use the cartridge and watch for poor print quality.  That is an indicator that the cartridge is nearly empty.  Don’t be tempted to force the cartridge to print more at this stage as you could damage the printhead.