Are you related to Rube or do you just admire him? Or you just do it because you can? Or no outlet nearby to plug into at night? All of the above?
Don’t think I’ve got any lights with powerbank function, but I did buy a pair of those USB charging/powerbank function 21700s from vapcell … but they get too hot and also don’t fit in a single light I own. So I don’t use them.
I bought one of the updated Wurkkos powerbank things (H1A) which stopped working about 3 days after it arrived… Replacement has been promised but yet to materialise…
Purpose-built powerbank I last acquired was a cuktech 10,000mah thing containing 2 x 21700s. I’m very happy with it, charging/discharging at c.30W is plenty fast enough for a smaller power bank.
How dare you suggest I compromise my flashlight!!!
Tried it one time for proof of concept then have never even thought about it.
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Somewhat often. It’s nice to have something on a long bike ride that can simultaneously be:
- Spare power for my phone
- A holder for a spare battery for my bike light
- Handheld lighting if I need it
I think I’d like a powerbank in a headlamp though because if I need light other than the bike light, it’s probably for fixing the bike.
I use it to power my display turn table when doing outdoor shots since I can’t plug into an outlet.
Yeah, when you can charge your gadgets straight on your head while driving bike. 
Standard 3535 20mm MPCB.
I used a Convoy 519A as recommended by @L4M4
I definitely recommend having something like this around but don’t stress your storage space/financials out if you don’t need to.
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You may want to check the Wurkkos HD20
It is a 21750 light, heavy as a headlamp. I have it and I love it, but I think of it more as an L light.
But, you can totally use it as a headlamp.
Forgive my ignorance as I don’t have any C-C bidirectional devices, how do you tell the device (e.g flashlight) you want it to supply current Vs charging?
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I gave my sister a flashlight that will jump start an automobile. Now there are flashlights that will charge a laptop.
There are jump starters with lights but there are no flashlights that will also jumpstart a car.
Edit
Flashlights, as we know them that will fit in some sort of a pocket. Just because it will fit in a glove box doesn’t make it a flashlight.
Not even once. And I have several lights that have the functionality. I have several battery packs specifically for charging my phone, if I need it
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This function is pretty gimmicky, but at the same time in an emergency could be a lifesaver. I’d prefer to have it and not need it than the other way around.
I’m guessing it’s a standard feature of whatever generic charging chip they’re using.
While charging devices from a headlamp I’m wearing is a funny image, the use cases are separate. During a bike trip, I might need a headlamp, and I might need to charge my phone. Minimizing the amount of stuff I need to do both is nice.
I said earlier that I only had 18650 lights that would do this but I forgot that I have the new wurkkos small lantern with a 21700.
It claims it will put out two amps and I suspect it’s pretty close to that.
Over the last couple of days I have experimented with three different phones and some other lights. I’ve not done enough to fully answer that question. To some degree it seems to be the device that has the most voltage will provide power. Other times it seems to be whichever device you plug in first will provide power.
The lantern will stop providing power with a resting voltage of 3.4v . I don’t know if it goes lower while in use and then is bouncing back to that or not. I believe that’s approximately where the wurkkos hd15 headlight stops providing power also.
Some of the phones will initially briefly display that they can’t be charged and you need to use the original charger. But then they will start charging. I’ve seen sometimes where they appear to be charging but they’re not really charging. I’ve experimented with different cables and gotten different results at different times also. All of my phones 1,4 and 7 years old will slow down the charge if the screen is on so it makes it difficult to fully determine how fast they are charging. So there are a lot of variables. I can’t get my USB tester into the recessed lantern port.
The devices figure it out themselves. There is multiple roles the devices advertise themselves with and then handshake it out between each other:
- Source only (wall chargers)
- Prefer source (Powerbanks)
- Neutral (probably flashlights)
- Prefer sink (cellphones)
- Sink only (devices without Powerbank capability)
These properties are either set in hardware, or defined in software of the devices, and they define which device power who if they are connected.
Many devices switch roles depending on their power state (for example if you connect 2 phones, usually the fuller one will start charging the less full one).
Sometimes a physical button can toggle source only or sink only to force the behavior you want. On an Android cellphone you can override what the phone negotiated in the notifications area.
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Partly related, I recently bought myself one of these (or similar) cables for about $3.50, mostly on a whim:
I did pick up a USB C tester at the same time but not used it much, the cable is so useful for plugging into ports to see how fast things are actually charging.
For example, I found my dell XPS work laptop will unwillingly do 14W ( sits at 7W and after 10 seconds negotiates a bit more) but drops to 7W if the screen turns off and then remains at 7W even after logging back in- explains why my phone was charging so slowly!
I connect them that way to drive both of them crazy trying to figure it out.
They hate me for it.
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