How long do 18650's last in storage?

[spinningmagnets]

I use 18650's for flashlights at work and at home.

I'm sure the duration for 21700's are the same as 18650's. If I find a good supplier, and buy a handful, then stick them in a cool, dark, dry place...

They arrive a 3.6V maybe 3.7V, so I assume that's the best shelf storage voltage.

If they still had 80% of their range after 20 years on the shelf, I'm OK with that. New, unused cells...

 

[dominik h]

Manufacturers say 0,5% to 1% loss per month.
But I think the loss is calculated from the actual capacity.

For example 3000mah battery you loose 1% from the full charged battery in the first month 30mah. In the second month you loose 1% from 2970mah. So it takes more than 100months until your battery is dead.

But I'm shure there are not a lot people which have tested this for more than 10years.

I have a few Li-NMC cells stored since 3 Years. They all had 3.55V 3 Years ago and last month they had all 3.53V. So not much lost in three years.
Storing is best between 30-40% SOC , if you store them with higher SOC they will age faster.


At work we have two machines which use a 18650cell for backing up the internal memory.
This cell is always held at 4,2V. It took 4 years and in both the cell was dead.

 

[Wattman]

Few know better than you spinningmagnets as you are a bit of guru about this stuff. I know 3 years in no problem.
Perhaps more pertinent, will you and/or I be around in 20 years? That is my personal greater concern.
A finer point on a more serious front, 'most' 21700 cells have more capacity than 18650 cells and that means 'if' the same voltage decay rate, the larger 21700 cells comprised basically of the same chemistry as smaller 18650 cells will last longer untouched hitting their min voltage. I wouldn't bet the farm but would wager a small amount. I think you know that and maybe were having some fun with the forum.

 

[Stealth_Chopper]

I think this is a current long term test relevant to your inquiry.

Calendar ageing tests of mixed cylindrical cells

"Simple" Calendar ageing test (at nominal capacity 0.2C) Test eqiupment: - Precision multi-channel battery tester (accuracy ±0.02％ // 10x better than ZKE testers) - Temperature chamber with ±0.1 °C stability - BF-2A four-wire cell fixture (20A version with Gold plated contacts) - Cells were...

endless-sphere.com

 

[fechter]

I have some packs made from 10 yr old Panasonic cells. I haven't measured the capacity, but I haven't noticed any significant change in performance.

 

[Wattman]

Thanks Chopper. Conventional wisdom of course that the 21700 larger capacity cells would have greater 'inertia' to loss.

 

[Hillhater]

Thanks Chopper. Conventional wisdom of course that the 21700 larger capacity cells would have greater 'inertia' to loss.

???…..what exactly does that mean,….and what is it based on ?

 

[Wattman]

???…..what exactly does that mean,….and what is it based on ?

There are many analogies between mechanical and electrical systems that manifest in mathematics.
I like to think of battery capacity as a heat transfer problem studied in thermodynamics.
Capacity represents thermal mass and is like a heat sink. Maybe you studied this in college.
If you have a bathtub of water at 50 deg's C and a glass of water at 50 deg's C and you subject both to zero deg's C or freezing temperature, which will freeze faster? The answer is, the glass of water. The reason is thermal mass. In mechanical systems, it takes more force to accelerate a higher mass. F = Ma. A body with more mass at the same speed has greater inertia.
I made the above comparison a bit dramatic, but you can do the simple math on the volume difference between a 21700 battery and 18650 cell and capacity difference is roughly proportional to the volume difference if both batteries have the same chemistry. Although not precisely linear, the reason why a 21700 cell has more capacity than a 18650 call is because 'its a bigger heat sink' metaphorically. With the same environment exposure aka heat transfer, the 21700 larger heat sink will lose its thermal mass slower even though this an analog to mAh's....same environment between a bathtub aka 21700 and a glass of water 18650.

Throughout electricity and mechanical systems there are analogs in properties expressed mathematically. Because I have studied both, I think in terms of inertia against loss when I consider a cell of larger capacity like the 21700 compared to the 18650.
YMMV of course based upon your experience.

In generic terms, a bigger battery is more resilient to loss whether it sits on a shelf or has a small amperage draw compared to a smaller battery with the same chemistry.

Here are some other mechanical/electrical analogs. There are many which is a fascination when using mathematics to describe physics which is pretty mind expanding to consider the uncanny relationship between electricity and mechanical systems:

 

[spinningmagnets]

Thanks for all the thoughtful replies. I read a lot, and if I find useful information from a source that seems trustworthy, I like to share it.

This was just a question that popped into my mind, and Google didn't seem to help.

 

[docw009]

I don't know about capacity loss, but bare new cells at partial voltage seem to hold their voltage for months, if not years.

I bought cells in November 2021 that were shipped at 3.42 volts. I still have a few stored outside in an old grill, with an ambient of -5F to 96F. and I just checked. Still at the same 3.42 volts. Some of these cells were probably made in 2019. The internal resistance also seems to be stable too.

 

[spinningmagnets]

Thanks!