I seem to have a different style of older cart from the one shown above.
I've been using the new carts for a few weeks now, I prefer them to the old style. The new style is the brown one on the left.
The new ones seem to be slightly longer and I'm guessing they hold slightly more liquid, but the biggest advantage to me is that they are a looser fit so I can just drop them into the mouthpiece, rather than having to press them down to the bottom with a paperclip or spare cart.
Air circulation is better so I get far fewer battery cut-offs (as I don't have to draw as hard/long).
I seem to be doing OK with the standard filler in the new carts, whereas I used PTB in the old ones.