Yes, carto screws on fine. As an example, my other batts all light up when the button is pushed, whether a carto is on them or not.. the light on this one now only comes on "sometimes"... as I said, more often NOT than does. At first I thought maybe the button was getting stuck, as I had that happen on my PT once.. but thats not the case here. Possibly the switch in the button is going out.. ?? Thanks, dohsma, for trying to help me. I did remember I had tossed a reg batt into my bag the other day just in case... Thank goodness, I have that to puff on! 