Probably a dumb question and already asked, but I can not find an answer :person_facepalming: …so here it goes:
Can I mix different brand of rechargeable 18650 batteries with the same mAh?…If not, please give me a quick and clear explanation since I’m not familiar with batteries performance.
Thanks guys!
If you want “quick and clear explanation” then just assume ‘no’ to be safe.
The real answer is that it’s complicated. Without knowing discharge curves for each cell and how exactly you are “mixing” them, it’s difficult to say.
Also, just because the same mAh number is listed on the cell by each manufacturer does not mean they actually have the same capacity.
Being Fenix and Olight batteries made specially for flashlight, I was thinking on using two Fenix and one Olight 18650 3500mAh batteries in a 3 batteries flashlight, but like you said before, they probably don’t have same or different discharge curves or the same capacity. But anyhow, I really appreciate your response and might as well stay on the “safe” side and just get another Fenix battery 
Battery age is also something to be mindful of. An old Fenix with many charge/discharge cycles on it may not have the same capacity and internal resistance as a new one.
Best practice is to buy 3 new identical cells and “marry” them to the flashlight and not use them for anything else.
Got it! :+1:
You also don’t have to buy Fenix batteries. Fenix doesn’t make batteries, they re-shrinkwrap their name on either Panasonic/Sanyo, LG, or Samsung cells.
Good example is, 3 Fenix ARB-L18-3500 batteries are $65.85. And 3 LG MJ1 3500mAh with Seiko protection circuits are $23.85. And I can guarantee you the protection circuits are better on these than the Fenix.
You have to be careful with Olight cells. Some of them are proprietary, and may not work in other lights. Olight does some weird things so their charging docks and magnetic chargers work.
depends if the cells are in series or parallel
parallel is no problem
if they are with PCB you can put them in series, as each cell has its safety board for overdischarge
They use very likely identical cells under the wrapper
It would be best to check their internal resistance and capacity with an analysing charger, if those are very close no problem
Would have to know which Olight cell and flashlight he has. He may have the proprietary cell with both positive and negative on one end of the cell, like this Olight requires, for the charger to work.
I have a new Eagletac MX30L3 flashlight and I understand I don’t have to buy Fenix batteries, but since I already have two batteries purchased from the Fenix Store about three two months ago, I might as well get one more for $22.00 - The LG MJ1 3500mAh seems like a good deal but I was recommended not to mix different brand of batteries.
Well, for a .90 cents more you could get 3 more, with better protection circuits. 1 Fenix is $22.95 3 LG’s are $23.85. But whatever. Sounds like you got it all figured out
I don’t need that many batteries but if you purchase my 2 Fenix 18650 I will sell them to you for $25.00 so I can purchase the 3 LG’s which, by the way, they are $27.14 once shipping is included.
You’re right. You can get 1 battery for 22, instead of three for 27 delivered. Go for it.
Take a step back…
Can you “mix” them… how?
Parallelled in, say, a Tomo battery pack? (Easy answer: yes.)
In series for a 2S light? (Easy answer: no.)
It’s important to know details before any meaningful answer can be given.
Is there a thread on the “why” (for series — since it’s where it matters)? Or what happens and its effects?
From the little I understand, this could affect the effective capacity if they are discharging in a different discharge curve, ie. the slower discharging (higher-voltage) battery will then be “charging” the faster discharging (lower voltage) battery.
Let’s assume we put a Samsung 30Q 3000mAh in series with a Panasonic NCR18650B 3350mAh.
My understanding is this would happen:
During the early part of the discharge of the 2 batteries in series, I would presume the 30Q stays at a higher voltage, while the NCR18650B sags more — in effect, the 30Q will try to “charge” the NCR18650B during the early part of the in-series-batteries’ discharge curve.
Now as the discharge continues, the 30Q will reach its capacity limit sooner as it has slightly less capacity, whereas the NCR18650B has still more life at the lower voltage portion of the discharge curve — thus, the NCR18650B will then be “charging” the 30Q during the end portion.
In effect, part of the the batteries capacities are actually used to charge each other (and thus less effective capacity to the device that’s using the batteries).
Is this scenario correct?
Sounds like you’re confusing series and parallel.
Parallel, you generally don’t care, as voltage across all the cells should be almost exactly the same.
Series, the one with the least capacity will be drained faster, sinking below its “I’m dead” voltage first, while the others still have charge to spare.
^Lightbringer,
you’re right, I confused series and parallel… I suppose I just described what happens in a parallel scenario…
For series, the bigger capacity won’t charge the smaller capacity battery…
Dta, what you write is wrong.
As pointed out, paralell no problem. You can even mix 18650 with 14500 in theory.
Series and all should be balanced.
Meaning same capacity and type with same age cells or with same discharge curve.
Protection boards on the cells should prevent any serious accident, but for cell life, runtime and safety don’t mix cells in series.
(unless you know exactly what you’re doing by analysing the individual cells beforehand)
Wellp, imagine a 1gal tank connected in series to a 5gal tank, both full to the top.
You drain ½gal from the series-connected tanks. The smaller tank is now at 50, the bigger tank is 90.
Drain another ½gal, and the smaller tank is empty, at 0. The bigger tank is at 80.
That’s bad enough for any cell, but continue to drain ’em, and the smaller tank will now be “reverse-charged”. Instant leak for alkies, bad news for NiCd/NiMH, supernova for Li.
With a low current load, mixing in parallel is fine but when you start asking for current that exceeds what the best cell can do, the best cell will do most of the work and have a short life. Its better to pair brand new quality cells if your pulling a heavy load and want the most life and capacity for the pack.
In series they need to be matched cells, its better to buy new and use those cells only in a group. If you buy 2 cells to use in a series cell flashlight, mark them and keep them as a pair. Reason being is what if you just use one of those cells for different things. That cell starts to degrade, the other cell is still like new. After a year of doing this now you stick them back together in that 2 series cell flashlight. There is a very high potential for a disaster. Over the years I have seen several post where batteries exploded in flashlights, most of the time it was a series cell light. If you search you will find plenty of stories of this happening.
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Watch this
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Its not very likely but the dangers are there. Better to be safe than sorry.
And don’t ever stick a flashlight in your mouth. :person_facepalming:
I see, so the “reverse-charge” is really dangerous. I previously thought it’s just bad for the battery life, so it’s not just bad for the batteries, but could actually be hazardous to use… Thanks for the explanations. I seldom see discussions explaining the theory (it’s often just “don’t mix different capacity/discharge curve” batteries in series, but I couldn’t understand the “why” part…) I think the above is clear enough for me.
~
Let’s repeat the above scenario, so if I use the 30Q and NCR18650B in series, now it’s possible that when the 30Q gets fully drained, the NCR1850B can reverse charge the 30Q, which may cause an explosion, right? Has anyone tried that scenario? (take safety precautions first before doing that experiment)
(not exactly related)
My multimeter uses 3xAAA batteries and I happened to have a pair of the same brand AAA and another single AAA different brand (all 3 AAA batteries are not rechargeable, and not alkaline). Now (nearly a year later), I notice my multimeter display sometimes flashes the screen when it beeps. I believe the batteries are now weak. Testing the batteries voltage, the 3 are not the same resting voltage.
So would it have been better if I had used the same brand AAA? (I just grabbed what AAA I had back when I got the multimeter — they were brand-new unused)