If your JC juices are 100% VG then you may have trouble using them in cartomizers. Check if they are (the site will say) and if so, I recommend you buy some thinner juices. I use PG juices with 20% or less VG in slim ecig cartos. The Volt cartos has looser stuffing and may work OK with 30% VG. Volt's own juices are (I think) 20% VG. I keep a carto damp with juice to prevent singeing and I can get a week or more use out of one carto. A simple plastic or delrin drip tip instead of the end cap is easy to remove to add juice or look at the stuffing (lotsa nice colors and types at LiteCigUSA.net). I add juice when the vapor seems light or dry, if the flavor is the tiniest bit wrong-tasting, if the carto is getting unusually warm. Before going out or putting a new battery on or just when I feel I haven't added juice for a while, I look at the top of the stuffing - if it has gone white/light I could add a bit of juice. I use thin clear juices that don't leave residue in the stuffing so after a week of use, my stuffing still goes white as the juice recedes.
For testing juices I recommend a sealed manual battery, standard resistance (not LR) DSE901 atomizer and 901 drip tip (same exact size as I mentioned above for use on a cartomizer). LiteCigUSA.net has the atty and drip tips. Just avoid acrylic drip tips (usually won't fit cartos though those swirl ones at LiteCigUSA.net have thin O-rings and may fit - I bought 2 and didn't try them yet)
Some general advice
(not personal - copied from advice I gave someone else)
Cartridges and cartomizers do NOT last as long as a pack of cigs unless you add eliquid
High VG juices are too thick for most cartomizers and tanks
Auto batteries or any battery with an open hole in the end can be damaged or killed by juice leaks
Manual batteries make it easier to get a good hit
100mah is about 1 hour of moderate vaping w/ a standard resistance atomizer or cartomizer
Slim ecigs should only use standard resistance - the hotter LR stuff is for the BIG models
Always charge an ecig on its own charger
never screw anything on or in any further than necessary to connect and work
You need spares for everything
New vapers don't buy enough eliquid