I am new to this forum and didn’t even realize there was a community like this. I don’t own any of the better brands yet, I own a bunch of Coast lights because until I started reading, I thought they were good.
Anyway, I have several lights that use the 3 AAA packs in them. I was tired of changing batteries, so I purchased some 3.7 volt 18500’s and used some O-rings on them so they fit in the light and don’t wabble around. It works just fine.
My question is this. Even though it is 3.7 volts instead of 4.5 volts, does the lithium ion have more amperage to make up for the less voltage (watts of power) And does an LED work that way? I may be imagining things, but I think it is a little brighter, or at the very least, just as bright.
And what about three non rechargeable lithium batteries, is that even more power (watts)?
What are the specific lights that you are talking about? As in model number?
Do you know for sure that the three AAA packs are wired in series? Have you measured them with fresh cells in them?
I have a few lights that use 2 of the 3 to 4 AA cell in parallel per pack. Giving 1.5 V. In other words each pack will replace a single C or D cell. Total 3 volts for the two packs.
If that is the case the two 18350 cells (Fully charged the are close to 4.2 v per cell) would likely fry the light at 8.4 V fully charged.
Would it take C cells. Maybe a pair of NiMH C cells would be better? Certainly more capacity and rechargeable.
Or even just replace the AAA Alkaline cells with AAA NiMH Eneloops or similar.
EDIT: After reading some other replies, and if you have lights that use a single pack with 3 AAAs in series, then the single 18350 would work. Read some of the other replies about Low voltage protection. I don’t know if you can get 18500 cells with protection circuits, but that could solve this problem.
Or just get some better lights designed for LiIon cells…
As you can see a 1.5V alkaline cell isn’t at 1.5V for long, and with higher current draw the voltage drops dramatically, this is due to the high internal resistance of alkaline chemistry.
A 3.7V li-ion cell range from 4.2V to ~2.8V, the voltage also drops at higher load but much less.
These 3xAAA (series) lights are usually direct driven with a series resistor to limit the current, on top of that resistor there is the internal resistances of the AAA cells, further limiting the current. With a li-ion cell that internal resistance is virtually removed and you usually end up with higher current.
I got a milk frother that takes triple AAAs, and bought some 18500s so I could stick one in there, and it works fine. They’re only 10bux or so, but I’d rather not toss it just because some alkaleak crapped the bed inside it.
But it’s a motor, not an LED. Circuits designed for those hateful AAAs use the internal resistance of those hateful little cells as a ballast resistor to drop the voltage and limit the current to the LED, whereas a Li cell has almost zero resistance in comparison. Might work great at 3.6V, but fry the LED at 4.2V out of the charger.
I wish Fasttech were still in existence, because it’d be easy to just grab a 7135-based driver (no µC, just the 7135s) and sandwich one in there to limit current evenly vs using a resistor. Of you can whip up one if you can get the parts.
The voltage difference isn’t as far apart as you think:
3 Fresh AAA = 4.5v(1.5×3)
1 Fully charged Liion is 4.2V
I too started out replacing 3×AAA lights with Liion batteries.
Here’s something you may/may not be aware of:
The lights designed for alkaline batteries don’t have LVP(Low Voltage Protection) because you run the light until the batteries no longer produce light or enough light.
Most Liion batteries shouldn’t be depleted below 2.75v or 2.5v.
If your 18500 batteries are unprotected, you run the risk of damaging the batteries in those type of lights.
Most of the lights I have now are designed for Liion batteries and have LVP built into the driver.
Well that is not an absolute rule!
There are places to use protected cells, and some applications where they can cause problems. The trick is to know the application and chose accordingly.
higher amperage lights often draw more than the safety circuit came provide. Also single cell use is much safer than series where they might not be properly matched. Most of the explosions happened years ago on questionable cells and vendors. We are generally much safer today with better tech. In your case experimenting, a protected cell is good sense.
Protected cells offer another point of failure. Plus they are added by who knows whom so it’s oftentimes unclear as to the circuit’s quality or installation.
For single cell lights with LVP, and if they’re charged on decent chargers, they’re not needed in my opinion
AND: As @texas_shooter mentions, Protection circuits will trip when using lights that draw higher currents than the protection is set for as max. Limiting the performance that we pay for.
Yes, the last three replies cover the situations where a protected cell is not the best option. I have something over 200 cells around here. Something over 100 lights. Maybe 10 of cells are protected cells.
But certainly in the specific situation that you have with the Coast lights, they should be used.
I have one of those Coast (LED Lenser) flashlights with 6 LEDs that someone gave me. I just compared it to my favorite budget CREE XML-6T flashlight that can be operated with either 3 alkaline batteries or a single 18650 battery. Both have aluminum cases and appear to be equally rugged. I’ve used my T6 flashlights as a bike headlight and for camping for a couple of years. I didn’t realize until now that the Coast light I have can not be focused. That alone would be a reason for my not buying one. It’s probably cheaper in the long run to buy new flashlights than to try to retrofit old ones that are meant for using only 3 alkaline batteries. I can still buy a similar flashlight on eBay for under $10. I don’t skimp on batteries though, preferring the NCR/Panasonic 3,400 mAh 18650 batteries. They run a lot longer than the cheap Chinese batteries that have inflated ratings. So, the short answer should be that the flashlight should be just as bright as using 3 alkaline batteries and because the mAh capacity for the single good brand Li-ion battery is more than what you can get from even good brands of alkaline batteries will run longer between replacing/rechartge the alkaline or recharging the Li-ion battery.
Why on earth would you want to buy non-rechargeable Li-ion batteries? That’s the advantage of the ones I use. I just got finished with rigging up a couple of small Halloween pumpkins that operate on three 1.5V button cells to work on one 18650 Li-ion battery. The lights in the pumpkins will work for many hours without my needing to replace the button cells. I will use them Halloween night when the kids come by for candy. Four pumpkins are wired to a single 18650 battery.
Speaking of AAA in series, I can think of one instance where it was fairly well done with AA batteries. The Nitecore EA4 Pioneer (which was later the EA41, and evolved to the EA42). Selfbuilt over on CPF wrote up a nice review, HERE.
Back in the day, the discussion was always about availability of replacement cell carrier should the original break. I’ve been on a search for a carrier for a while and not found much.
Backstory is I have a vintage radiation meter which uses obscure alkaline battery consisting of 4S AA cells welded to +/- terminals on each end. Looks like a chunky D - cell but at 6V.
I’ve DIY’d one of those plastic “cube” AA cell holders, reused the metal end plates of the original battery as terminals. Just looks a bit rough and would prefer a pre-made adapter, problem is, none of these cell carriers are available separately!
I’ve recently acquired some 26650 cells so will give them a try, might be too long though…
