Staying with drippers? Unregulated tube, box or REO. Adding a nice rebuildable tank? High power regulated. The nice regulated box with quality Kayfun (or similar) experience is something worth having. Also, 2 batts in series gives you 8.4v. In parallel it's still 4.2v with more available amperage and capacity. Go regulated and get a nice tank you can build. You already have all kinds of dripper, mech stuff.