Yes, you can refill your gas cylinder even if gas is still remaining inside. First, remove the cap from the bottle. Next, measure the amount of gas remaining in the bottle. If the gas remains inside the bottle, you can still refill it. Third, remove the screw from the top of the bottle. Once removed, it is still possible to see the blackness inside the bottle. If the bottle is still wet, it may be possible to remove the screws by hand. Finally, turn on the bottle and measure the pressure. If the bottle has been refilled, it should now be at least 1.3 psi.