Yes, most external batteries should be charged on an external charger, unless the mod manufacturer specifically recommends a USB (which the Provape Radius does, but the design is such that to continually remove and replace batteries would likely break the mod, eventually). Even if the manufacturer says you CAN charge via USB, that is true but a) it's going to take a fair amount of time, b) it tends to cause wear and tear on the USB port so you have to be careful and c) in two battery mods, charging can occur unevenly between the batteries.
The good news is that a decent one can be had fairly inexpensively and I MUCH prefer swapping out batteries rapidly and letting them charge (with one eye out on their status) externally, and putting a fresh one in.
I use a Nitecore Intellicharger 2 at the moment, it has some issues, but it's been a solid charger (just have to be careful with the slides) but there are other manufacturers who do a good inexpensive 2 or 4 bay charger as well.
Best of luck,
Anna