I’ve got a nice hand sized, “Zoomie” flashlight. It has a three battery regular AAA battery cartridge that with fresh batteries yields over 3+ volts. I’ve noticed the battery cartridge is nearly the size of one 18650 battery. I’m tempted to try that out for perhaps longer battery life. Would I harm this zoomie with the 18650 ? Thanks.
There’s a good chance it will kill the flashlight. It’s probably a cheap flashlight without current regulating driver and so it relies on the internal resistance of the batteries. A Li-ion battery will provide too much current.
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I’ve done it a bunch of times successfully. Haven’t burned out a light…yet. 
The 3AAA type device SHOULD go extinct in my opinion.
3xAAA=4.5v to start. BUT…current output IS limited.
lithium=4.2v to start. But…current is NOT limited (nearly as much). Burnout is possible. But hey, it’s probably a cheap light, right?
The critical issues are:
length-you may need magnets to make it reach. There are a couple different types of 3-AAA holders.
Diameter-I use plumbing O-rings to shim if necessary.
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Hi flydiver… You are on the mark here. Length doesn’t appear to be an issue; The cartridge is nearly the same length as the 18650’s - Panasonic’s. I would need to use O-rings for diameter makeup. 4.2v is my setpoint for charging my 18650’s on a Xtar, VP2. As I vaguely recall, one of my daughters bought the zoomie, a “Ghost Vapor” and probably spent too much for it. I dropped a 18650 into it and turned it on for a moment or so and it worked better than the AAA battery cartridge. I do wonder what you mean by “4.2 lithium, current is not limited.” * I’m a newbie to all this, but attentive and want to learn. KawaiBoy, a former or perhaps still current poster here turned me on to the world of L.E.D. flashlights and my own experience from buying poorly made house led security lights, etc., have shown me how much I need to learn. Suggestions along those lines would be greatly appreciated if you would. Thanks for your efforts. ~D
Li-ion batteries can deliver more power than a set of AAA batteries.
When a load like the LED is attached to a battery, its voltage will drop depending on the current. An LED needs a specific voltage to draw a specific current. If battery and LED are matched, they will find an equilibrium – this would be called “direct drive”. This is what happens when you use AAA batteries. But the voltage of a Li-ion battery won’t drop that far and the LED would be driven at a too high current. In this case you need a current limiting (regulating) driver between the battery and the LED.
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Yes, you can use an 18650 just fine. The LED Vf is probably pretty high, and the drover circuit probably uses cheap transistors and would absorb the extra voltage as heat (BTW, most 3 AAA carriers are over 4 volts in my testing, 1.5 volts x3 unless using under charged NiMH or nearly dead Alkaline).
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Thank you. I’m going for it and hoping it doesn’t burn it out. It certainly is brighter, and should have longer battery life.
Most likely true, but there are caveats.
Figure a 3AAA alkaline is in series, therefore 4.5v TO START with maybe 800mAh capacity. But it’s ability to output current is compromised so the battery drain is slow. It might run a good while.
The lithium starts at 4.2v, but has a much higher capability to output current, as long as the LED and circuit can deal with it. Thus, a brighter light. But the brighter light is at the expense of pulling the capacity out faster.
Most likley the 18650 will have a higher to much higher capacity. But if it’s a ‘puny’ 18650 with lower to modest capacity (some of the uber cheap Chinese batteries are awful, like 300-500mAh) it could drain faster, thus might have shorter but brighter life.
If it claims it has 9000mAh, I can guarantee you it’s not better, it’s awful.
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As previously pointed out: the 18650 may output too much power and fry the LED. If you’re extremely lucky, with an old 18650 with very low discharge rate and very high circuit resistance within the flashlight, you might achieve enough voltage sag that the LED is safe.
But also, these lights generally have zero heatsinking for the LED, with no shelf under the MCPCB. So more power could desolder the emitter, and in the worst case, cause a short and kill the driver.
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Another thing to consider: There’s probably no low voltage protection in the flashlight. Only use protected Li-ion batteries with it.
The analogy I use to understand is voltage is like water pressure and current/amps is the volume.
Higher voltage (pressure) can push more volume (amps) and a bigger water supply can provide more volume before the pressure drops.
I think these two comments are worth repeating:
Generally I’d discourage you from putting random cells in random lights. Convoy has some very affordable options which are well reviewed and have LVP (low voltage protection) and are designed to run on lithium.
What cell(s) are you using? I hope they are something reputable if you like your house…
The xtar charger is good though.
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The internal resistance of a battery is like the size of the drain in a bucket. If you connect a big hose (an LED) to the small drain (AAA batteries), not much water will flow through it, independent of the pressure.
But if you cut a large hole in the bucket (Li-ion battery), the bucket will be empty in no time (and you will stand in a puddle). To prevent that you need something to regulate the flow (the driver).
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V=IR, so with more pressure you can push more current through the “hose”.
We are on the same page though, I find it far easier to understand something I can “touch” than abstract concept of electrons whizzing around.
Yeah, “independent” was not specific enough. Both buckets (1x Li-ion and 3x AAA) have the same size and thus pressure (voltage), but one has a large and the other one a small hole. You need a way bigger bucket to get the same flow rate with the small hole.
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Hi: I have some random cells, but considering the knowledge of the person I got them - kawiBoy, a former or still active poster here, I’d guarantee they are high quality. I cannot see any I.D. on some of them, but one I or kawiboy marked “4.35” on the side of. Several others have ‘QR’ codes on them and I.D.'d as ‘Samsung’, INR18650 -30Q, Samsung SDI, 136. I purchased several others when I bought the xtar charger. I was advised and bought 'Panasonic’18650 3.7v, 3000mAh. Also, I bought a ‘Convoy’ C8, and a flame-thrower (short term) of a flashlight - a ‘Sky Ray’ which requires four 18650 cells all aligned in the same positive direction. (Is that parallel or series ? Yes that’s how little I know). Short term meaning it won’t sustain the highest setting very long without getting warm to hold. I’m thinking in the longer term, I may need a new contactor plate (?) where the positive poles rub against it; Looks something like a bullseye target of red, silver, red concentric circles for contact / non-contact, and JB-A with four circling positive signs on the bullseye, red center. The silver circle shows some degradation or wear chunks missing. I might be able to send a picture… Have to figure out ‘how’ to do that via iphone. Thank you…
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That’s somewhat more understandable Sammy. Still not clear enough yet to ‘visualize’ though. I can relate to your condition regarding the difference between conceptual vs visual / touchable. Contradictory as well in my case. In many things, such as economics, I can make good sense of the concepts to the point of becoming my Econ. professors prize student. Yet some things I find more difficult to get my mind around. Econ, if you don’t know, is very abstract. There must be some way or source that provides a more visual breakdown. Maybe the ‘water hose’ analogy could work with appropriate labels and visual aids.
@d_house You can use a program called Local Send. Put it on your phone and computer. Allows you to send files to other devices on your network. Works quite well for the 4 computers and 12 other devices with either ios, android or windows on my network. By network I mean connected to the same wifi/internet. LocalSend - Downloads
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Thank you; That’s a ‘new thing’ to me. Is it a ‘safe and non-bloat’ thing ?