How long does a 18650 battery last?

Yea, how long does it last?

At what? Runtime, lifetime, something else?

Lifetime, I mean battery life.

Fenix Elite said:

Lifetime, I mean battery life.

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Battery life can still mean two things;
(a, runtime) How long will it last on a single charge, and
(b, durability) how long until it's wore down, and needs to be replaced with a new one.

A, runtime: Really depends on how much of a load you put on it. Typical runtimes are often between 45 minutes and 250 hours or so, but there's a lot of variation. Also, 2 hours of runtime might mean it'll last someone about a month or three for example, if it's not used too frequently. A lot of lights these days have different modes, draining the batteries at different speeds. That also means the same light could last between 1 hour and 100 hours, depending on how you use it.

B, durability: Somewhere between 6 and 36 months perhaps. I'll typically buy 2-3 batteries with anything new (if I don't have enough batteries for it from before), and then buy another 2-3 batteries a few months after that, just to have replacements ready at hand. There's a huge variation here, some will ride their batteries really hard on a daily basis, others will just have a low load on the once in a while, and so on. I budget for replacing them every 6 months – a bit pessimistic – with the intention of having a small stock of them, and then slowing down purchasing, to not let new batteries age too long on a shelf.

And please do note that I'm just throwing out some numbers to give you a bit of a ballpark impression here. These numbers are not intended as "the" truth, and I'm sure we could run into a heated debate about these things. You won't have to look far to fine something outside of those numbers, or someone that'll disagree with them.
I'm trying to draw up a picture of ballparks here, nothing more.

terjee said:

Battery life can still mean two things;

...
B, durability: Somewhere between 6 and 36 months perhaps.... I budget for replacing them every 6 months – a bit pessimistic – with the intention of having a small stock of them, and then slowing down purchasing, to not let new batteries age too long on a shelf.

And please do note that I'm just throwing out some numbers to give you a bit of a ballpark impression here. These numbers are not intended as "the" truth, and I'm sure we could run into a heated debate about these things. You won't have to look far to fine something outside of those numbers, or someone that'll disagree with them.
I'm trying to draw up a picture of ballparks here, nothing more.

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I've got a couple of very lightly used 18650s that I've had for at least 18 months; I don't have a charger that gives remaining capacity, but subjectively, the flashlight stays on about as long as it used to. Six months sounds like really frequent replacement. Laptops used to be run by 18650s and they had to last at least until the next release of Windows came out. I'd like to think my expensive battery purchase will last something like the 8 year warranty on a Tesla car, which is made of 18650-size cells. On the other hand, many a phone or pod hits the recycle bin when its lithium battery no longer works well.

My NiMh D cells are basically useless after only 4 years, maybe letting them (mostly) sit on a shelf was a bad idea. That was an expensive purchase, too, but next time I buy I'll make sure to *use* them.


What are people seeing in practice? Probably varies all over the map!

Bill

I'm still my NCR18650 cells from 2013. I typically keep them charged around 4.05v. These don't get used often; I keep one in my headlamp which gets used for about 30-90 minutes on backpacking trips about 10 times every year. They're still doing fine, but I wouldn't know for sure unless I ran them down or did some extensive testing.

I'm guessing the internal resistance is a bit high, so not the best for high load applications. Runtimes are probably decreased, but again, I wouldn't know since I never run them down below 70% or so.

Kitchen Panda said:

Six months sounds like really frequent replacement.

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Yeah, I don't think most average users will see anything that low.

Also, it's quite common to think of the lifetime of a cell as lasting until it has 80% capacity left. If you're a both a light and occasional user, 80% is probably like new from a perceptual perspective, and even 60% would probably be fine. All of that said, I'd personally lean towards replacing them at least every 3 years or so (three years of use that is). LiIon-cells are inherently a bit scarier than NiMHs etc, so erring on the side of caution is tempting.

10 years+ -- with reduced capacity. Almost forever. But it begins to lose capacity the day it's made. I have had only a few 18650s fail. The very old and original 2200 mAh AW cells. they drastically lose charge after being fully charged.
I also have very old 2600 mAh AW cells that keep working.

So, you get a few hundred cycles under optimum performance and then a very long decline. I discard a cell if it quickly loses charge after being fully charged. Charge it to 4.2V or so then 2 weeks later it's at 3.9V. discard.