Is your e-cigarette a 2-piece (battery + screw-on cartomizer) or 3-piece (battery + atomizer + cartridge)?
If 3-piece, you can refill those cartridges with
eliquid. If the cartridge pushes over the atomizer then it may have a recessed juice cup. If the juice cup is recessed then sticking an unbent small paper-clip in the mouth hole should push it up for refilling.
If 2-piece, cartomizers are disposable but most can be refilled for 3-4 days or more. If the mouth-end cap pops out easily you can add
eliquid to the stuffing. But you have to take the cartomizer off the battery first and be really really careful to clean up all drips and make sure it will not drip before putting it back on the battery. You probably have automatic batteries (drag to turn on) and you can kill those with a juice drip.