the only problem i've had is when the carto "feels" like it's totally screwed on but it's not. (the XL batt i have had some "burrs" on the threading) i sanded down the burrs and now no prob on the cartos. before i sanded previously i just "eye-balled" the gap between the batt top & the carto bottom and kinda forced it to screw down further & that fixed it. i'm sure that the threading issue could also be on the cartos same as the batts