I know! I know!
Any cartomizer with a Kr8 fitting should work just fine. The Echo carto has huge capacity and is, of course, relatively huge in size so it looks a bit weird on the VOLT battery.
My favorite cartomizer (of any model) is CigEasy's Kr8-compatible
Elite 808, which I recently
reviewed. It is 2ml capacity, so approximately twice that of the VOLT (or most Kr8) cartomizers. The reason I
love it, however, is because of its fantastic performance (vapor, TH, and flavor), including on the VOLT battery. The Elite carto is slightly wider than that battery, but, to me at least, it doesn't look too strange.
You could pick up a
$15 five-pack to try out. If you fall in love as I have, then you may want to get the
$50 kit, including two 380 mAh
batteries (slightly longer and wider than the 78mm VOLT batts), which integrate seamlessly with the Elite cartos.