Watch carefully if you buy an i4 charger, some include the DC cord, others don't. It's about $5.50 separately.
The 18650's in the Amazon link say 2 in the package, if I'm seeing the same deal. Sometimes Amazon redirects you, though. The page I was on also listed the combo with the i4 for $15.05 more under 'Frequently bought together', no DC cord (separate i4 link):
http://www.amazon.com/Nitecore-IntelliCharger-i4-Battery-Charger/dp/B005UAI372/ref=pd_bxgy_e_text_y
Some good US sellers:
http://www.e2fieldgear.com/panasonic-ncr18650b-3400-mah-protected-li-ion-battery-single-cell/ (Use code BLF)
http://www.e2fieldgear.com/keeppower-3400mah-li-ion-protected-18650-battery/ (Use code KEEPPOWER for 20% off)
RMM's sales thread:
https://budgetlightforum.com/t/-/22440
If you go with Tenergy, get the Premium or Centura rather than the green 'economy' cells.
If you don't mind the length, the TR 3T6 runs great on 8 AA NiMH's with 3 extra extender tubes available from Banggood, cut a sleeve from .5 inch electrical conduit to prevent rattling, cover with heat-shrink or a couple of pieces of tape on the ends.
http://www.lowes.com/pd_72711-1792-101543_0__?productId=3129551
or
http://www.lowes.com/pd_118909-1792-807256_0__?productId=3127645 (fits in car)