Is 4.0V on a lithium battery really 80% charge?

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Bort
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Is 4.0V on a lithium battery really 80% charge?

According to conventional wisdom and many sources lithium battery charge percentages can be determined by their voltage.
Its different by battery but for many it goes something like (no load)

3.6V empty
3.8V 40%
4.0V 80%
4.1V 90%
4.2V 100%

But i find when i charge my batteries to about 4V i don’t get a lot of juice compared to full charge which should only be 20% more but seems to be more then that

And when charging my cell phones they reach 80% at 4.2V, then stay at 4.2Vish from 80-100% (constant voltage charging).

So how does this work, if 4V is 80% then switching from constant current to constant voltage happening at 4.2V makes no sense.
And in general battery voltage does not fall much when taken off the charger.

Thoughts?

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Docware mapped the SOC vs voltage of several cells :


(voltage measured 20min after each 5% discharges)

Correllux
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I've always wondered how people arrived at those % figures as well and if they were applying them specifically to typical voltage needs in the circuit or what, but it never quite made sense to me.  Compounding that are several lists/charts that vary all over the board.  I've always heard about 3.2 was "empty" and freeman's chart seems to concur.  But that also makes me wonder about all of the manufacturer white sheets that typically list 2.7 or 2.8 on the bottom end.  I guess technically - and at the very low discharge currents they use - there is still juice flowing.  I just try to recharge at or before 3.2v for most cells, and wish more lights that have LVP indication or shutdown would bump up a bit higher than 3v as a threshold. 

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thefreeman wrote:
Docware mapped the SOC vs voltage of several cells :


(voltage measured 20min after each 5% discharges)

Very interesting, where is this chart from?

Though i am still not convinced, when charging does this hold or only on discharging?

Like i said if a charger switches to CV at around 80% then its doing so at 4.2V then sticking at 4.2V till full charge. So how does one determine the SOC between 4.2V just going from CC to CV and 4.2V 100% charged?

Or maybe you have to wait till 4.2V and it does settle once taken off the charger but only in the CV stage?

Next time i throw the phone on the charger i’ll take a screen capture at 80% and its voltage.

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thefreeman
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Here is the discharge curve form these tests :

it bounce back up a lot especially at low SOC.

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percents are guesstimates

I rely on voltage, not percents

here is my version of the percent rule of thumb, but I dont go by that:

3.1V empty
4.1V full

each .1 is worth 10%
so 4.0 =90%

but I recharge if a battery goes below 3.6v (50%), I dont wait until it is empty. My fresh charged batteries, on my DMM, read 4.1+ but still below 4.2

> i find when i charge my batteries to about 4V

why would you intentionally undercharge?

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My phone uses a 4.35V battery.

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Bort wrote:

Very interesting, where is this chart from?

Though i am still not convinced, when charging does this hold or only on discharging?

Like i said if a charger switches to CV at around 80% then its doing so at 4.2V then sticking at 4.2V till full charge. So how does one determine the SOC between 4.2V just going from CC to CV and 4.2V 100% charged?

Or maybe you have to wait till 4.2V and it does settle once taken off the charger but only in the CV stage?

Next time i throw the phone on the charger i’ll take a screen capture at 80% and its voltage.

From this thread (docware is also user on BLF)

This is a discharge test, but similarly if you unplug during CV phase it should settle at a lower voltage, it depends on the internal resistance of the cell and the current applied. Only when saturated (end of CV phase), it will stay at the same voltage (well it still drops a little bit).

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jon_slider wrote:
percents are guesstimates

I rely on voltage, not percents

here is my version of the percent rule of thumb, but I dont go by that:

3.1V empty
4.1V full

each .1 is worth 10%
so 4.0 =90%

but I recharge if a battery goes below 3.6v (50%), I dont wait until it is empty. And my fresh charged batteries read 4.1x

> i find when i charge my batteries to about 4V

why would you undercharge?


Because storage at over 80% charge ages batteries much more quickly. I want to charge to 80% to get most of the capcity but keep my batteries in good health longer.

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The lower the internal resistance of the cell helps the battery hold more capacity to a lower voltage. This will also come into play with load (resistance) while in use.

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Bort wrote:
storage at over 80% charge ages batteries much more quickly. I want to charge to 80% to get most of the capcity but keep my batteries in good health longer.

storage is for storage

before using a battery that has been in storage, it should be brought up to a full charge, because the storage voltage is close to just 50% capacity

so, for USING batteries, they need to be fully charged

otherwise, if you use batteries that have been at storage voltage, you increase the risk of overdischarge, And you dont get “normal” runtime of a fully charged cell.

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Full charge doesn't hurt so much especially if you use a lower current (all smart chargers do, tapering down as the cell approaches full voltage).  80% is better for li-po and the packs in phones, yes, but I don't think that applies so much for our cells.  For storage - like weeks and months of disuse - sure, pull them off or drain them down around 3.5v or somewhere close...similar to what the manufacturers recommend in their white sheets.  For regular use, full charge, use 'em and enjoy 'em, and realize that you aren't really damaging the cell that way because it's in regular use and not holding at full (overfull) capacity for long periods of time. Similar to very low discharge voltage...generally not horrible as long as it's not for an extended period of time or at high current (or repeatedly). 

Now you have to stop and wonder whether "100%" on your phone screen is actually 100% of charge on the actual battery...many phones lie about that, but it's fine.  They're generally programmed to control charging in smart ways for the health of the battery.  But the 4.35v of most phone packs vs our li-ion at 4.2 ....slightly different world with different characteristics of the cells.  Not entirely interchangeable. 

I'm less concerned with lithium than I am with my NiMH which take more babying to ensure longer life and retained capacities. 

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jon_slider wrote:
Bort wrote:
storage at over 80% charge ages batteries much more quickly. I want to charge to 80% to get most of the capcity but keep my batteries in good health longer.

storage is for storage

before using a battery that has been in storage, it should be brought up to a full charge, because the storage voltage is close to just 50% capacity


I have not explained well, i meant for normal everyday use i charge to 4V.
I tend to not use my high power lights much so they can be at 80% for weeks or rarely months for the rarely used lights.
My most used light is the Moon RC2 which has built in charging, it charges at 1A and has a 2.2Ah battery so i charge it for 1.5H from low voltage warning giving me about 75%ish.

Quote:
so, for USING batteries, they need to be fully charged

otherwise, if you use batteries that have been at storage voltage, you increase the risk of overdischarge, And you dont get “normal” runtime of a fully charged cell.


This is incorrect.
Risk of overdischarge is mitigated by low voltage warning on most modern flashlights. Charging to less than 100% just gives reduced runtime. But storage at over 80% accelerates capacity fade.
I am using almost 10 year old 18650s that have over 95% of their original capacity.

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Correllux wrote:

Full charge doesn’t hurt so much especially if you use a lower current (all smart chargers do, tapering down as the cell approaches full voltage).  80% is better for li-po and the packs in phones, yes, but I don’t think that applies so much for our cells.  For storage – like weeks and months of disuse – sure, pull them off or drain them down around 3.5v or somewhere close…similar to what the manufacturers recommend in their white sheets.  For regular use, full charge, use ‘em and enjoy ‘em, and realize that you aren’t really damaging the cell that way because it’s in regular use and not holding at full (overfull) capacity for long periods of time. Similar to very low discharge voltage…generally not horrible as long as it’s not for an extended period of time or at high current (or repeatedly). 

Now you have to stop and wonder whether “100%” on your phone screen is actually 100% of charge on the actual battery…many phones lie about that, but it’s fine.  They’re generally programmed to control charging in smart ways for the health of the battery.  But the 4.35v of most phone packs vs our li-ion at 4.2 ….slightly different world with different characteristics of the cells.  Not entirely interchangeable. 

I’m less concerned with lithium than I am with my NiMH which take more babying to ensure longer life and retained capacities. 


Storage time at over 80% accelerates capacity loss according to many sources including battery university. This has even been confirmed by Tesla which allows you to choose a maximum charge percentage in their software.

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Well, ok.  Do what you will.  As alluded above, the definition of "storage" is different than what most of us, and it sounds like you, too, do with our lights and batteries.  Keep in mind that temperature has a lot more influence here than SOC.  For longer term, take both into account, sure, but also realize that the level of potential degradation is pretty small really. 

For your purposes, I'd ignore the chargers, just trust your multimeter and keep the cells at the voltages you prefer that way.  Seems like a self-imposed limitation but if it's worth the slight hassle to you, hey no harm done.  Smile 

Probably should note that my perception here is coming from one assuming healthy cells of relatively recent manufacture.  If we're talking about old tech (which Battery University was founded on and hasn't quite updated much over the years) or well used laptop pulls and such, some of this matters a little more I guess.  Old "chemistries" being a little less resilient in some ways.

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> it charges at 1A and has a 2.2Ah battery so i charge it for 1.5H from low voltage warning giving me about 75%ish

maybe

have you put a meter inline with the charger?
have you measured the battery voltage after you stop the charge?

my charger tapers way down as the battery charges…

> Charging to less than 100% just gives reduced runtime. But storage at over 80% accelerates capacity fade.
I am using almost 10 year old 18650s that have over 95% of their original capacity.

ok, do whatever works for you

with all due respect, your strategy of undercharging in order to “save” battery life is not my personal style

I want to use batteries with a full charge.. I dont care how many years they last.. I just charge them up and use them.

I also do not “store” batteries at half discharge..
I store batteries fully charged, so I can use them when I need to change a battery

I have not had any unusual battery expenses, none of my LiIon cells have stopped working normally. They are only 5 years old though… you have much older batteries than I, but you have never let yourself enjoy them at full capacity…

my most recent battery purchase was to replace some 5 year old eneloop pro that no longer provide full brightness. On my light meter they make half as many lumens as my same age eneloop white… so I bought a few more of the white ones…

5 years of carefree charging and using… not bad, either way

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jon_slider wrote:
> it charges at 1A and has a 2.2Ah battery so i charge it for 1.5H from low voltage warning giving me about 75%ish

maybe

have you put a meter inline with the charger?
have you measured the battery voltage after you stop the charge?


I wish i could, its a sealed unit.

Quote:
my charger tapers way down as the battery charges…

Yes, theis is going from constant curent up to 4.2V to Constant Voltage at 4.2V to full charge.

Quote:
> Charging to less than 100% just gives reduced runtime. But storage at over 80% accelerates capacity fade.
I am using almost 10 year old 18650s that have over 95% of their original capacity.

ok, do whatever works for you

with all due respect, your strategy of undercharging in order to “save” battery life is not my personal style

I want to use batteries with a full charge.. I dont care how many years they last.. I just charge them up and use them.

I also do not “store” batteries at half discharge..
I store batteries fully charged, so I can use them when I need to change a battery


I charge to 4.2V full if i am going to use it the same day but all my lights have batteries at 4V until LVP tells me to recharge.

Quote:

I have not had any unusual battery expenses, none of my LiIon cells have stopped working normally. They are only 5 years old though… you have much older batteries than I, but you have never let yourself enjoy them at full capacity…

my most recent battery purchase was to replace some 5 year old eneloop pro that no longer provide full brightness. On my light meter they make half as many lumens as my same age eneloop white… so I bought a few more of the white ones…

5 years of carefree charging and using… not bad, either way


Oddly enough i don’t care about NiMH, they are practically solid state, i charge them to full regularly and abuse them and they work great even 10 years later.
That said i have heard the Eneloop Pro are not as robust as the standard Eneloop, people have said 2-3 years later they are not doing as good as new.

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> i have heard the Eneloop Pro are not as robust as the standard Eneloop, people have said 2-3 years later they are not doing as good as new.

yes, its a tradeoff
the Pro have more capacity, at first, but they also die sooner

I treat my LiIon the way you treat your Eneloop…

refrain:
Use it up… Wear it out… Make it do… Or do without

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jon_slider wrote:
> i have heard the Eneloop Pro are not as robust as the standard Eneloop, people have said 2-3 years later they are not doing as good as new.

yes, its a tradeoff
the Pro have more capacity, at first, but they also die sooner

I treat my LiIon the way you treat your Eneloop…

refrain:
Use it up… Wear it out… Make it do… Or do without


I have not owned any Eneloop Pro so never had to baby them.

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I gave this some more thought and i am going to test this by fully charging a battery, discharging it to 4V then recharging it to see how much juice it takes up.
Then i will drain it, charge it to 4V, let it rest then charge it to full.

See if the numbers are similar.

The Journal of Alternative Facts TM

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Some tool batteries only charge up to 4V per cell or 20V in 5S config, yet they still claim full capacity. Maybe because if they charged all the way up it will take 50% longer in the CV phase and probably degrade the battery when stored full.

The batteries from my Mavic air drone will auto discharge to 3.8V after not being used for a couple days.

Could be just perception but I store batteries with relatively low cycles at 4.2V for months at a time and after a while I notice they don’t stay very long at 4.15V+ after removing from the charger, the capacity however doesn’t drop more than 10% when tested (4.13 vs fresh cycle).

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Bort wrote:
I gave this some more thought and i am going to test this by fully charging a battery, discharging it to 4V then recharging it to see how much juice it takes up.
Then i will drain it, charge it to 4V, let it rest then charge it to full.

See if the numbers are similar.

Figure out what rate you’ll discharge at.

Capacity should never be expressed without an accompanying discharge rate.

Chris

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ChrisGarrett wrote:
Bort wrote:
I gave this some more thought and i am going to test this by fully charging a battery, discharging it to 4V then recharging it to see how much juice it takes up.
Then i will drain it, charge it to 4V, let it rest then charge it to full.

See if the numbers are similar.

Figure out what rate you’ll discharge at.

Capacity should never be expressed without an accompanying discharge rate.

Chris


I’ll use the same light.
I am not interested in the empty to full battery capacity, i am interested in how much juice goes in when discharged from 4.2V to 4V and charged up to 4V then charged to 4.2V.

I suspect they won’t match.

The Journal of Alternative Facts TM

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