It’s splitting hair, but the graphs seem to show that storage at too high temperature may be more detrimental than storage at too high voltage (if one has to choose).
1 Thank
Different brands may behave slightly differently, but generally yes. Note also that 50% storage number that gets thrown around is just the “optimum storage voltage”.
Storage anywhere under 4.20 is better than completely fully charged, obviously as you approach “optimum” which is about 3.7v, you have a trade off with stored amount of energy.
Most of my lights are single cell, so I don’t have to worry about balancing them. I tend to keep my cells at (very roughly) 4-4.1v but I’m not pedantic about it.
This all said, cell life might not bother some if new cells are readily available and fairly inexpensive.
What would be a typical voltage of fully charged battery?
4.20V is fully charged.
3.7v is approx 50%
3V (especially under load) is empty.
1 Thank
Cheers! In the meantime I found this general graph:
p.s. The %capacity vs. OCV seems to decrease slowly, roughly linearly within 4.2V(100%) to 3.5V(10%) range, but the voltage dives quickly to less than 3V level afterwards. I suppose that the moral is that anything near 3.5V and below means spent.
Most liion cells we use are more linear than that.
For example Samsung 30Q 18650:
/Samsung%20INR18650-30Q%203000mAh%20(Pink)-Capacity.png)
You can get power from the cell all the way down to below 3V, but 3V LEDs run at ~3.3V at full power, so single cell flashlights will start to lose the high modes or fade in their output around there, unless the flashlight has a boost driver and a 6V or greater LED, or if it’s got a buck driver and 2s cell config, etc.
2 Thanks
Keep in mind those graphs, I think I’m right in saying, are not showing permanent capacity loss. I think. Just based on the numbers. They took the battery out of storage, threw it on a discharger, and measured what was left. That’s different from permanent capacity loss.
Obviously it relates to permanent capacity loss. We know that high temperatures and high SOCs are not ideal for long term storage. But the effect is probably not be as significant as those graphs indicate. If you ran those same cells through a couple cycles and capacity tested all of them again from a full charge, the high temperature high SoC ones would probably still have less capacity but it might be by 1% and not 10%, or whatever
Actually…I’m looking at those graphs again…that might actually be permanent capacity loss…so ignore everything I just said lol
1 Thank
Other way around 
There is an article at the Battery University that I’m reading now on the very topic:
3V under load is empty…?
3V under load can be anything. Depends on the load. You could be overcharged and see 3V under load if it’s heavy enough.
3V at rest is empty.
You are wrong. You can read the paper here.
“Test procedure.—To monitor the degradation of the cells, a uniform checkup procedure was performed periodically at 25◦C for all cells. As listed in Table II, this checkup comprised a constant current (CC) charging step with a low charging current of 100 mA for DVA and a constant current constant voltage (CCCV) discharging step to measure Cactual.”
This published article takes an extremely deep dive into the details about lithium ion battery degradation issues. It is long and tedious reading. They cite all the sources. They explain what’s going on when you start nearing 100% SOC and why that is bad and why it’s bad to let it sit at 100% SOC. They also explain that not all of this stuff is understood. I doubt you’ll find a more comprehensive article on the issues. If you want the short version just search the internet for why EV automakers and phone makers recommend that the battery is not regularly charged to 100%. From everything I’ve read in many places
4.0v seems to be a sweet spot where self-discharge is not a real big issue and you avoid the problems created as you get towards 100% or 4.2v.
And you’re not really giving up much capacity.
They are looking at degradation issues way beyond just a full charge. Here is the long published paper from Royal Society of Chemistry Lithium ion battery degradation: what you need to know - Physical Chemistry Chemical Physics (RSC Publishing) DOI:10.1039/D1CP00359C
1 Thank
I dont think Samsung shows it. Apple uses some algorithm as most people dont plug it in at zero.
Beat you to it lol
I was looking at those graphs again like, wait…how many days are in a year?..55°C?..wait a second… 
On Android I use an app called Accubattery Pro. It gives lots of good data on charge/discharge cycles and battery health. But, of course, it only starts tracking from when you install it. It tracks wear in “cycles” Which I assume is charge from zero to full. For instance, most nights I charge from maybe 65% to 85% (I have 85% set as the max charge). It shows 0.22 cycles for that.
Anyway, it is free if you want to play with it.
I have the Pro Version 
I’ve used that a lot.
But I don’t leave it installed on my phone. Its uses too much battery lol
I’ll install it for a few days, see where my battery is at, then take it off. I like the app, but because it has to stay running in the background constantly monitoring your battery usage it ironically ends up using a significant chunk of battery itself lol. It’s aging your battery just a little bit faster.
I cant remember how I did it, maybe they got rid of this feature, but there used to be a secret screen you could access that would tell you exactly how many cycles your battery has ever been through in its life. Maybe it’s gone now, idk
Oh, pro tip. If you leave that protect battery feature on for a long time, like 6 months or whatever, it kinda messes up what your phone thinks it’s 85%. At least for me it did. After 6 months 85% turned into 95%. I disabled it and charged to 100% and it only took like 150mAh to get that 15%. The math didn’t work out, it’s showing I have 4000mAh capacity still.
But if you turn it off for a few weeks and then turn it back on it seemed to remember where 100% was again.
I known they did at one point, you had to do some secret thing to access that screen but I know for sure it was there I checked it a few time. But it’s very possible they got rid of that but that like 7 android versions ago
I typically run the phone down to maybe 15% then fully charge it to 100% … maybe once every couple of months…
I just started using the 85% limit on this phone I got recently. I used to just do it manually on my old phone… letting it on the charger until it hit 82% to 85%. That thing showed about 82% battery capacity after around 5 years. So I guess I did something right.
Thanks for the tip.
Empty depends on the actual chemistry, many modern cell chemistries works fine down to 3.0V. Some older chemistries starts to get damaged at that voltage. Where you have to be careful is below 3.0V. some of the older chemistries get dangerous, more modern chemistries can handle lower voltages without serious problems (I wrote a article about that).
Phones and other advanced devices usual use a advanced charge monitor chip. It has a couple of rules build in, they are designed to make the device as safe as possible and not to be 100% precise. I.e. following the advice of the chip/device will keep you safe (in most cases), but may cost you a bit extra.
4 Thanks