Stupid Idea, Just haven't found it, ahead of the curve.

[Locki]

So just got my latest shipment of torches.
Nightcore LA10 AA
Klarus G20 26650
FiTorch P25 26350 (if you need a small light that can push allot of light )

Anyways my thoughts are really about the Klarus G20. With how huge the battery is in this light I'm curious why you couldn't have more options in the light in terms of a battery bank. Heck I shelved the stock battery that it came with and put an Orbtronic IMR 26650 30A 5750mAh battery in it.
1. Change out the head or tail with a USB charger for a portable power source. Kind of removing the light option or tail switch with a USB port for power access.
2. Have a USB-C port that can be used for charging or discharging. ( really want Micro USB to go extinct I hate that port)
3. Just have a light with a full size USB plug for charging things.
I can understand the argument that if your carrying a flashlight you don't want to tap into its power source but who only carries one flash light in reality. I also can see how it might effect the water resistance rating but I've got several lights that have ports build into them for charging so I can see a work around for this. I even have one light that has the charging port inside the light. You just unscrew it to get to the port.
Even to have the nice housing of one of these flashlights without the light as just a portable power source would be really nice in my opinion.

 

[Poppy]

Not a stupid idea.
I am pretty sure that I have seen one or two 18650 lights that can also be used as a power bank. IMO a cell phone and the ability to communicate is more important than a light. Besides, the LED in the cell phone would probably be less demanding on the battery (due to lower output) than the led of the light, should you need to use the cell phone led for light.

 

[thermal guy]

Yes there are quite a few flashlight out now that can be used as a power bank.

 

[Locki]

So I just haven't found one yet, at least a good one at least. I eventually remember this little guy UCO Pika LED Lanturn has that feature, the battery is just so small it sucks... unless you need enough juice to make one call. I'll have to do more digging around to see if I can find a decent 26650 light with this feature.