As batteries get a little old, sometimes the center piece in the battery (on the threads side) gets pushed down with usage. This is specially true for our Vertigo, Mirage, and Geneva batteries. So when you screw in your cartridge, there may be little or no contact between the battery and cartridge metal parts. This may result in no vapor and it might seem that the cartridge is a dud.
Helpful Tip: Place a small pin (like a push-pin or needle) in the space between that center piece and the thread walls around it. Then incline the pin at an angle and try to lift up the center piece a little. With the pin at an angle, go around the center piece couple of times. You would see that the center piece has now come up a little. Now screw on the cartridge and you might find that your dud is suddenly working.
We recommend when charging your battery that you do not screw the battery into the charger too tightly. If you see that the center piece in the battery appears to be pushed down, use the method mentioned above to restore it to the original position.