I personally like the Provari 2.5 with the extension so I can use the 18650 batteries. I'd recommend 2 batteries at the very least. They have a kit you can order. If you want to check them out you can click my banner. There are other good mods at less cost such as Sigelei, Vamo, SVD (has firing button issues), Tesla, MVP2 (internal battery), VTR (box mod) DNA 30 (box mod), and others I can't think of at the moment. All but the MVP2 will require external batteries and a charger just like the Provari so consider that cost when looking at them.