I mean that, depending on how they are used, they eventually either get clogged up and hard to draw on, or the coils burn out. So they don't last forever. The juice in them stays good for months, maybe a year.
You can use certain clearomizers with slim batteries. The best one I've seen and used that will work on a slim battery is the Fluxomizer from Gotvapes.com. If you get these, make sure you get the 808 version in 2.4-2.6ohms. Clearomizers last longer than cartomizers. They are cleanable and you can change juices in them. They taste better as well. I don't use regular cartos anymore since I started using Fluxos. They really don't cost much more than blank 808 cartos either.
You are severly restricted in what you can use with a small battery. You have a narrow range of ohms that you need to stay within, and a big tank or something is kind of silly and impractical on a little battery. If you want to move up, the Volt's X2 battery will give you a lot of options you don't have, (including a passthrough), with a little battery. Meanwhile, the Fluxomizers are the best thing to stick on the end of a slim battery.