Actually the T13 or T08 resistor mods seem the best way to go for you - cheapest and you get some real power out of them. I always prefer batteries in parallel then serial, so I would prefer the T08 - also for the more compact size. I think they are in the same price range, about $27.
I also suggest finding viffers link to the 22 turn pot in the zy-t08 review thread, get a spare pair of hands to help with the meter rig and you can dial in to your exact desired drive current. 
There is a 3x18650 light but it only has a C8 size reflector
Search for usb charger flashlight, sorry can’t past links on my phone
Nope!
The 7G9 won’t come close to comparing to the TN31.
I saw that zeng something flashlight on fasttech and became super excited. Then I saw the other garbage they added to the light. 
Yep - one review showed the 7G9 @57kcd and the TN31 is supposedly ~120kcd. My 7G9 was closer to 70kcd, mod'ed of course.
But it almost looks like a TN31 
. If you could find one close to $60, maybe not bad. Think the 7G9 is eliminated anyway... Cost is the driving issue, it appears.
The 7G9 I have I would bet is putting out around 70,000 to 75,000 lux. The best TN31 I have is putting out 115,000 lux according to ma_sha1 who I bought it from on his light meter. No comparison in throw vs the two at 100yds.
Even the Crelant 7G5 V2 collimator head won't beat the TN31 in throw. Let's do a mouseover.
And trust me the TN31 whips the Crelant 7G5 V2 collimator head even more in throw the farther out you go. Even my camera agrees with what my eyes see.
Case in point
220yds
Yep , the TN31 stock is a true beast! Think it runs @3.5A, but they got a whole bunch of other things right in that design/build, considering it's just a U2.
Ok. So i have to correct myself. I didn’t realized how large the TN31 is. I can see why it out throws so well. What i was originally looking for is a smaller hand held light that accept 3x18650 or 2x18650. The TN31 is rather long like the typical 2x18650 long lights. The USB 3x18650 light looks rather interesting. Maybe get one of those and plug the usb ports with epoxy. Looks like it comes with a 2.8 amp driver. The small sun zy-t08 is still an interesting light for the price and could use a cheap resistor mod.
Can’t go wrong with the Small Sun T08 or the Small Sun zy-t 13!! I’m already ordering 2 more of the T08’s just cause I really like it… And for $25 bucks a pop it’s a no brainer!! Oh and I’ve got a bunch of C8’s and not a one comes close to beating the T08!! Good luck!!!
ZY-T13 is a good bang for the buck. I got one and thought it was good out of the box. Even better when modded with a simple 20 cent resistor.
There is also This One on CNQG . I think ChicagoX likes it.
The HD2012 can run a 18650 also, and comes with a battery sleeve to do so, so you don’t have to get new cells. It is a very nice powerful light, but not pocket sized.