I swear - I'll never understand this .... there must be a market for them, cause places make them, and people buy them.. but honestly, in this situation, why people would want a "rechargeable" flashlight, that needs to be recharged via a USB cable and port, (that's out in "the field" which I can only assume means they won't be near utilities), REALLY confuses me.. when you'd need to buy and carry what's basically "another battery pack" to recharge "the other battery" in the flashlight, just doesn't seem efficient or logical to me. You're literally charging one battery from another using a cable, and waiting an hour or so to do this at least, when you could instead buy a good flashlight that runs off of standard batteries, and just buy a plastic case and carry 2, 4, 8, (ect) extra batteries that are ready to go in seconds.. it's not like 6 AA batteries will inhibit anybody that's already carrying stuff with them.
I can understand the concept of having some rechargeable things, and taking an external pack that can recharge stuff like a cell phone, or gps that might have internal batteries that can't be swapped out, or arent available at the general store, But I'd personally wanna keep that stored energy in an external pack for those important things, instead of having sometimes simple like a flashlight become a parasite to it. If the external pack goes bad, then nothing works. Lose the USB cable, nothing works.. flashlight dies in the middle of the night when you might need it, and then you have to wait for it to charge..
Sometimes keeping things simple is just better.. that's just my 2 cents.. not directing this at the OP - but you hear about people buying "survival" stuff, and then opt for the most expensive, brightest, smallest flashlights they can find, - that only last 2 hours, take the most uncommon batteries on earth, and cost more then a case of military grade MRE's.. I just don't understand the logic, but that's just me..,