# What is a better way to charge and discharge single LiFePo4 cells at high current?



## sparx-262 (Nov 24, 2011)

Hello dear forum members,

I am planning to perform various test of single LiFePO4 cells that have a capacity of around 100 Ah (in the future the capacity may be more).

The plan is to perform various C rating charges and discharges on different manufacturer batteries.

It was planned to discharge the batteries with CBA-III and CC400 discharger (http://www.rcgroups.com/forums/showthread.php?t=938266), but apparently new CC400 will be available only in february 2012. So a decision was made to use the CBA 500W amplifier (together with CBA-III it can discharge at 160A constant current http://www.westmountainradio.com/content.php?page=CBA). 

After that I was looking for a device to charge different single LiFePO4 cells but I ran into a problem because I cannot find a right device to charge the cells.

There are three options that I have so far:

1) Buy a *Heavy Duty 25 Amp Power Supply* like this:

http://www.mcmelectronics.com/product/TENMA-72-7670-/72-7670

It has a constant current and the voltage can be changed, I assume that I will need to change voltage because some batteries have a CUT-OFF-VOLTAGE at 3.65V and some at 3.8V.

The problem with this is that it outputs constant 25A and I cannot change it. Therefore I assume that I can only charge cells at 25A. But I want to perform charges with different current.

2) Buy a *HCS-3400 Power Supply 1-15V DC / 0-40A* like this. (0-60A is also available ant the model is HCS-3600)

http://www.energonsolutions.co.uk/ProductListDetail.asp?FileB2BArticleDetailID=2042529

I would allow me to change voltage and to change the current and I think that this is the right device.

But there is one thing that is bothering me. How will I be able to say when the cell is fully charged? And isn't it dangerous to charge cells with devices like this (thinking about possible outcome like: overcharging, explosion, destroying the cells because there is no charge algorithm and the "power-supply-charger" does not know when to stop)? 

Maybe there are other aspects that I did not take into consideration. So please be so kind and comment 

3) And the last option so far is the *ICharger 3010B*:

http://www.amainhobbies.com/product...fe-NiMH-NiCD-DC-Battery-Charger-10S-30A-1000W

It can charge batteries up to 30A (don't know if it need additional components to do that ). And I think that this device is the safest of all the mentioned options.

So guys, do you think it will be possible to perform some tests with this kind of equipment?  and if so, what devices is it better to choose? And if you know of some chargers and dischargers or maybe even systems that can do both at high current, please write their names and post some links, because it will be very interesting to read about them and find out about new stuff .


So please guys, leave your comments and suggestions! Thanks!


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## kd8cgo (May 2, 2009)

It's funny you mentioned this combination of equipment, because I picked up a CBAIII, CC 400, and the iCharger 3010B for this exact purpose this summer. I have been very happy with all the equipment so far, and it all works very well for this purpose.

I did not consider the 500W amplifiers offered by West Mountain Radio as I considered them a bit too expensive at the time.

The iCharger needs an external power supply or battery on its input to function, it has DC input leads. I am using it with a 13.8V/23A DC supply I already had, but this limits my total output below the 3010B capability. If you want to use it in discharge mode, it is limited to 80W discharge, unless you have a battery to use a 'current sink' on the input, in which case it can be used as a charger in reverse and dump the energy back into your battery on the input side. There is also a linear voltage curve in the manual you need to consult if you want to use the full 1000W charge potential, you'll need around 24V on the input to reach that power level IIRC.

All in all I think these are probably the best common tools for making your own battery bench test rig, they do become less useful as you try to test larger and larger batteries, but they still provide the DIY'er with very functional testing capabilities.


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## EVfun (Mar 14, 2010)

sparx-262 said:


> [...] would allow me to change voltage and to change the current and I think that this is the right device.
> 
> But there is one thing that is bothering me. How will I be able to say when the cell is fully charged? And isn't it dangerous to charge cells with devices like this (thinking about possible outcome like: overcharging, explosion, destroying the cells because there is no charge algorithm and the "power-supply-charger" does not know when to stop)?


If you set the voltage and current it will charge at the set max current until it reaches the target voltage. At that point the only way to not exceed that voltage is for the current to reduce as needed to keep the cell voltage from rising. This is what is needed for a basic Lithium charger. 

The commonly used Manzanita Micro PFC charger is charger works like this, plus the ability to start an adjustable timer when the the constant voltage phase is reached. It also offers a number of other options chosen by a row of DIP switches. The down side is that the minimum charging voltage is about 12 volts.


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## GizmoEV (Nov 28, 2009)

You will want to stop the charge when the current drops to 0.05C if you are using the 3.65V ending voltage. You will need to use a lower ending current for lower ending voltages. Unfortunately I had to give my test cells back before I could collect data to map ending current vs. ending voltage so I can't give you numbers.


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## brainzel (Jun 15, 2009)

GizmoEV said:


> You will want to stop the charge when the current drops to 0.05C if you are using the 3.65V ending voltage. [...]


Why did you choose 0.05C @ 3,65V and for which cell?

CALB f.e. says "0.5C Q 3.6V" charger disconnect ...


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## DIYguy (Sep 18, 2008)

Consider the Powerlab 8 from Revolectrix. It's an amazing charger. 1344 watts. Actually, it's much more than a charger, they call it a battery Work Station. It will do all the main battery chemistries, is customizable, can do 40 amps and when charging from a battery pack will do regen. I just started using mine to test some cells and it's very kewl. Does graphs for IR as well. There are a lot of options. It will do a lot of what the CBA does as well.


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## dtbaker (Jan 5, 2008)

why don't you just rig some pv cells and a charge controller to set the top voltage.?


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## GizmoEV (Nov 28, 2009)

brainzel said:


> Why did you choose 0.05C @ 3,65V and for which cell?
> 
> CALB f.e. says "0.5C Q 3.6V" charger disconnect ...


The spec you listed is the charging current. I'm talking about how to know when 100%SOC is reached. If you have plenty of time and let the current taper to 0A then you can charge to 3.4V. If you charge to 3.6V you need to stop when the current drops to 0.05C otherwise you will overcharge the cell. You can easily tell if a cell is overcharged by letting it sit for a day or more and check the terminal voltage. If the voltage is over 3.4V then the cell has been overcharged.

For various reasons I had my charger set to taper current down to about 200mA at the end of charge. Because of this I lower the ending voltage to 3.465vpc and my cells always come up at 99-100%SOC.

Also, there is very little energy in the cells above 3.4V. If you test some cells out you will find the same thing. This is true for TS LFP cells and from what I read is the experience of others using CALB cells.

If you insist on charging to 3.65V and letting the current taper to near 0A you will be shortening the life of the cell. Why do that?


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## DavidDymaxion (Dec 1, 2008)

I ran an Optima lead acid battery through a Harbor Freight battery tester (the adjustable 500 Amp one) to a lithium cell. Then I could charge as high as 500 Amps (you need to fan cool the HF battery tester if you do that). The adjustable battery tester let me vary the current. I watched the cell with a voltmeter and IR thermometer to see when it was fully charged. You can also use the HF battery tester for high current discharges. I wore ear plugs and safety googles when I did this, plus I put a tarp between me and the batteries, just in case one popped.


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## dougingraham (Jul 26, 2011)

They seem rarer these days but what I am using is the Vicor Megapac's for my single cell test charger. I have adjusted a 5V 40A module down to 3.6V. With this I can charge at 40, 80, 120, 160 if I add booster modules. The max you could go if you had 7 booster modules would be 320 amps. I programmed a PIC to control the cutoff when it sees the current drop to 5 amps (100AH cell) and used an EV200 contactor as the cutoff device. I am using a 60A hall sensor I got from Digikey. The contactor was simpler to use than several FETs in parallel.

I have been trying to buy more of these booster modules but the used sources on EBay seem to have run out.

Best wishes!


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## sparx-262 (Nov 24, 2011)

kd8cgo said:


> [...] The iCharger needs an external power supply or battery on its input to function, it has DC input leads. I am using it with a 13.8V/23A DC supply I already had, but this limits my total output below the 3010B capability. If you want to use it in discharge mode, it is limited to 80W discharge, unless you have a battery to use a 'current sink' on the input, in which case it can be used as a charger in reverse and dump the energy back into your battery on the input side. [...]


That's great that the our choice of equipment almost matches 

Can you name the charge and discharge characteristics that the iCharger has when connected to a 12V 55Ah lead (Pb) car battery and if using the regenerative function?

And is it possible to monitor the characteristics of cells with CBA while they are being charged by another device?? 




EVfun said:


> If you set the voltage and current it will charge at the set max current until it reaches the target voltage. At that point the only way to not exceed that voltage is for the current to reduce as needed to keep the cell voltage from rising. This is what is needed for a basic Lithium charger.
> 
> The commonly used Manzanita Micro PFC charger is charger works like this, plus the ability to start an adjustable timer when the the constant voltage phase is reached. It also offers a number of other options chosen by a row of DIP switches. The down side is that the minimum charging voltage is about 12 volts.


So as I understand in order to charge a single cell with a constant current and constant voltage supply (f.e. like the *HCS-3400 Power Supply 1-15V DC / 0-40A*) I and need to manually monitor the voltage on the cell terminals and manually lower the charging current (f.e. from 30A to 1A) when I reach the desired cell voltage (f.e. 3.4V) and then charge at low current(f.e. 1A) until the cell voltage is exactly (f.e. 3.6V) ? 

P.S I think the Manzanita Micro PFC is a no-go for single cell charging because of the minimum 12V charge rate. 



DIYguy said:


> Consider the Powerlab 8 from Revolectrix. It's an amazing charger. [...]
> Does graphs for IR as well. There are a lot of options. It will do a lot of what the CBA does as well.


Yeah! Very nice device i must say! I just spent a lot of time reading about it and trying to play with the CCS software  I have done some comparing to the ICharger 3010B and the I can say the following things.

Pros:
*ICharger*
~100$ cheaper than PowerLab8
Battery temperature sensing
Maximum charge and discharge current: 30A 
*PowerLab 8*
Can be controlled and programmed from PC
Creates an internal resistance graph and calculates the average.
Maximum charge and discharge current: 40A
Ability to set time for the cell to cool down while performing cycle tests.

Cons:
*ICharger:*
Not configurable from PC.
Shows cell internal resistance on display but not on graphs (maybe it does show IR on graphs but I could not find it )
Software is half English half German .

*PowerLab 8*
No battery temperature sensing

So it seems to me like the 100 extra dollars give some more features to play with, however could not create new charging presets (I am guessing that maybe it was because the Power Lab device was not connected to the pc and therefore the software did not allow me to create new presets. Or maybe not, I cant be sure because I don't have this device )

In overall now I will have to make a decision between the two and the PL8 seems more interesting but I also need to monitor the temp of cells while i test them and therefore I will probably choose the ICharger just because of the temp sensing feature. 



dtbaker said:


> why don't you just rig some pv cells and a charge controller to set the top voltage.?


Not exactly sure what you mean 



DavidDymaxion said:


> I ran an Optima lead acid battery through a Harbor Freight battery tester (the adjustable 500 Amp one) to a lithium cell. Then I could charge as high as 500 Amps (you need to fan cool the HF battery tester if you do that). The adjustable battery tester let me vary the current. I watched the cell with a voltmeter and IR thermometer to see when it was fully charged. You can also use the HF battery tester for high current discharges. I wore ear plugs and safety googles when I did this, plus I put a tarp between me and the batteries, just in case one popped.


Can you post some links to the tester that you are using? 



dougingraham said:


> They seem rarer these days but what I am using is the Vicor Megapac's for my single cell test charger. I have adjusted a 5V 40A module down to 3.6V. With this I can charge at 40, 80, 120, 160 if I add booster modules. The max you could go if you had 7 booster modules would be 320 amps. I programmed a PIC to control the cutoff when it sees the current drop to 5 amps (100AH cell) and used an EV200 contactor as the cutoff device. [...]


That interesting! So when the current drops to 5 amps you just stop the charge? Wouldn't that mean that your batteries end up not fully charged?


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## dougingraham (Jul 26, 2011)

sparx-262 said:


> That interesting! So when the current drops to 5 amps you just stop the charge? Wouldn't that mean that your batteries end up not fully charged?


0.05C at 3.6V is often considered fully charged. 5A on a 100AH cell is 0.05C. If you let it go the current is dropping fast at that point. It is only a few minutes to get to almost zero current. A lot of people will tell you that it is overcharged if you let it go that far.


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## sparx-262 (Nov 24, 2011)

dougingraham said:


> 0.05C at 3.6V is often considered fully charged. 5A on a 100AH cell is 0.05C. If you let it go the current is dropping fast at that point. It is only a few minutes to get to almost zero current. A lot of people will tell you that it is overcharged if you let it go that far.


I will have to agree with you on this one 

Can you adjust the output current on each charging module ?  

Also can you post some links to the charging modules that you are using?


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## DIYguy (Sep 18, 2008)

sparx-262 said:


> Yeah! Very nice device i must say! I just spent a lot of time reading about it and trying to play with the CCS software  I have done some comparing to the ICharger 3010B and the I can say the following things.
> 
> Pros:
> *ICharger*
> ...


I don't have experience with both however, the PL8 has a more precise internal resistance monitor and also higher current balance than any of the others. It's apparently faster also (according to RC guys). I would ask Jozzer, he has a lot of experience with these things and has built many packs and tested many (thousands) of packs.

Cheers.


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## dougingraham (Jul 26, 2011)

sparx-262 said:


> I will have to agree with you on this one
> 
> Can you adjust the output current on each charging module ?
> 
> Also can you post some links to the charging modules that you are using?


The Vicor's have a master module and then you can parallel booster modules. The booster modules exactly share the output with all the other modules they are paralleled with. The only module you can adjust is the master. There is no current control. You get some multiple of 40 amps depending on how many cells are in parallel. Ive paralleled 2 modules to get 80 amps but could do more. For safety and consistency I have done all my charge testing at 40A.

Just search Ebay for Vicor Megapac. Vicors web site is www.vicr.com.

For a while you could get the MegaPAC's with 8 interesting modules for about $60 but those deals are less available now. New prices on these are as much as a couple of thousand dollars so $60 is a bargain.


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## Sunking (Aug 10, 2009)

You are going to want to use a variant of a float charger with automatic cutoff when charge current tapers down to a set percentage of the C rating of the battery.

When first energized the battery voltage will be below the set float voltage and fold back to a constant current mode. Once the battery reaches the set point voltage will hold there. and the current will start to taper until it reaches a point you need to set to terminate the charge. I think LiFePo is 3% of C


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## EVfun (Mar 14, 2010)

sparx-262 said:


> So as I understand in order to charge a single cell with a constant current and constant voltage supply (f.e. like the HCS-3400 Power Supply 1-15V DC / 0-40A) I and need to manually monitor the voltage on the cell terminals and manually lower the charging current (f.e. from 30A to 1A) when I reach the desired cell voltage (f.e. 3.4V) and then charge at low current(f.e. 1A) until the cell voltage is exactly (f.e. 3.6V) ?


If you have set the voltage limit in advance (usually done when you charge your first cell) you don't have to turn the current down because the power supply will do that as needed to keep from exceeding the preset voltage. How well, and safely, that works depends on how accurately the power supply can regulate the voltage. A quality adjustable power supply should work as a CC-CV charger for a single cell with you only needing to shut the unit off at the correct finishing current.


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## sparx-262 (Nov 24, 2011)

dougingraham said:


> The Vicor's have a master module and then you can parallel booster modules. The booster modules exactly share the output with all the other modules they are paralleled with. The only module you can adjust is the master. There is no current control. You get some multiple of 40 amps depending on how many cells are in parallel. Ive paralleled 2 modules to get 80 amps but could do more. For safety and consistency I have done all my charge testing at 40A.
> 
> Just search Ebay for Vicor Megapac. Vicors web site is www.vicr.com.
> 
> For a while you could get the MegaPAC's with 8 interesting modules for about $60 but those deals are less available now. New prices on these are as much as a couple of thousand dollars so $60 is a bargain.


A very interesting choice to perform high amperage charging 

I am also thinking on testing the cells at different charging currents to see how they react and to see what is the best charging current for different batteries so a choice between only 40Amp or 80Amp kind of adds some limits the research. Furthermore a I believe that the recommended charging current for a LiFePo4 batteries is 0.3C, so for a 100Ah battery 40 Amps would be to much. And a 20Ah battery would be tested that would make a 2C charging current, and I guess that would damage the battery in some way. 



Sunking said:


> You are going to want to use a variant of a float charger with automatic cutoff [...]


I believe that chargers are programed to work like this. However will it work with a power supply? 




EVfun said:


> If you have set the voltage limit in advance (usually done when you charge your first cell) you don't have to turn the current down because the power supply will do that as needed to keep from exceeding the preset voltage. How well, and safely, that works depends on how accurately the power supply can regulate the voltage. A quality adjustable power supply should work as a CC-CV charger for a single cell with you only needing to shut the unit off at the correct finishing current.


Thanks for the explanation EVfun  I have just received good news from West Mountain Radio. It appears that the CBA-III device can also monitor the cell while it is being charged and graph Voltage vs Time.

Therefore I will simply choose the HCS-3600 (http://www.manson.com.hk/en/dcpowersupplies_detail.php?m=1&id=10) as a charging device and the CBA-III as a discharging device!  

This way I will be able to set the needed voltage and needed current for charging and then discharge with parameters that I select in the CBA software.

The company representative also told me that there is a way to perform cycle tests, but he said that some extra equipment is required, so that is still yet to come 

So guys, do you think this will work?


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## sparx-262 (Nov 24, 2011)

Hey guys!

Finally all the equipment has arrived! 

The charger is working perfect. I have already tried charging CALB, Winston and Sinopoly 100Ah LiFePO4 cells @ 30A. The charger automatically switches from CC to CV when the battery is almost full. I turn it off when current drops below 5A because I have read somewhere in this forum that the charger should be disconnected when current is below 0.05C. Can someone confirm the "0,05C charger disconnect" rule? Because I was looking throug the specifications and did not find anything like that. 

The analyzer is working nice, but I already had problems with it. Since the Amplifier that came with the CBAIII did not amplify current I had to try and discharge each battery with the CBAIII alone. At the very first attempt the analyzer stopped working because inside of it was a 25A fuse that was blown by the current. After replacing the fuse with a 40A fuse I tried the discharge again. Even thou it is capable of discharging at 40A, just at 25-30A discharge rates the analyzer gets to hot and turns of itself after aprox. 15 minutes. So now I'm stuck with a 20A discharge rate until the amp will be repaired.

I have seen a lot of different pdf´s for Winston 100Ah batteries and I am confused. It is written that the operating voltage is max4.0-min2.8V, however the deep discharge voltage is 2.5V. ThunderSky pdf (whitch i believe is the same battery as Winston, I am talking about the original 145 mm :145x68x217: battery) claims that the operating voltage is max4.25-min2.5V

I don't know who to believe and I am confused.

Can some one write the charge and discharge cutoff voltages for the following batteries:

Sinopoly (black, size:145x62x217) 
CALB (blue, size:145x68x217 ) 
Winston (yellow, size:145x68x217)

Will I damage a sinopoly cell with discharge 2,8V cut-off voltage if i discharge it to 2,5v or even to 2,0v ? 

Thanks in advance guys!


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## dougingraham (Jul 26, 2011)

sparx-262 said:


> Can some one write the charge and discharge cutoff voltages for the following batteries:
> 
> Sinopoly (black, size:145x62x217)
> CALB (blue, size:145x68x217 )
> ...


These are all basically the same chemistry and can be treated the same. Charge to about 3.6 volts per cell with a 0.05C cutoff. Going to a higher voltage will add almost nothing to the charge. If you drop the CV point to 3.5 volts it will take a little longer to charge but not too much extra.

A single cell of any of these will suffer very little damage if taken down to zero volts. You probably don't want to leave it there very long but I have taken them to zero in tests and see no difference in capacity afterwords. The problems occur when you reverse them. There is very little energy left in the cell when you get down to a little under 3 volts per cell at low currents. If you are pulling high currents from any of them it is easy to see the voltage sag below 2 volt when there is plenty of charge left in the cell. This will not harm the cells. The discharge cutoff is something that doesn't mean much with LiFePo4 chemistry cells. 

There are only a few things you need to worry about with LiFePo4 cells. Don't overcharge them. Don't reverse them. Don't let them get too hot. If you put your hand on a cell and you cant hold it there then the cell is probably too hot. Don't try to charge if they are too cold. If you stay away from the end points they are supposed to last longer. My own plan is to only charge to 95% full and stay above 30% on discharge. Voltage won't tell you the state of charge in a way that is useful. You need to count amp hours in and out.

Don't worry too much. These cells are rugged.

I hope that was useful.


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## sparx-262 (Nov 24, 2011)

Thanks for the reply! 

However from the manufacturers specifications the voltages of cells seem very different, e.g.:

name: charge cut-off - discharge cut-off voltage
Winston: 4,0V - 2,5V (2,8V (80% DOD)) 
CALB: 3,65V - 2,5V 
Sinopoly: 3,8V - 2,8V 

I mean that these numbers are written definitely for some reasons. In the winston specifications it is also written that the cell is damaged if the voltage drops below 2.5V

And also correct me if I am wrong , but I assume that if I charge Winston and Sinopoly cells to only 3,6V they will end up not fully charged.


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## dougingraham (Jul 26, 2011)

sparx-262 said:


> Thanks for the reply!
> 
> However from the manufacturers specifications the voltages of cells seem very different, e.g.:
> 
> ...


You can find different numbers from the same manufacturer as the years pass. They start out higher and go progressively lower for the charge cutoff voltage. For all the LiFePo4 cells it looks like you could set the CV point to 3.45 volts and float the cells there without any damage. Essentially they never quite get fully charged at that voltage. Anything above that and at some point you will get to full charge. For the discharge cutoff in my testing there is no measurable damage from taking them down to zero volts as long as you don't leave them there very long. You are looking at almost no energy left in the cell at low currents when you get down to much below 3 volts. At high currents you could have a considerable amount of energy left in the cell even if you pick 2 volts as your cutoff. This is why voltage under load doesn't mean much.

Once you wire cells up into a battery the pack voltage divided by the number of cells means little unless you have done some sort of balance. For the charging end this would be a top balance. In this case all the cells would finish charging at about the same time. Small variations in balance would give rather large differences in the individual cell voltages. For discharging you want to have the cells balanced at the empty point. If your pack is in bottom balance then you don't risk cell reversal when someone inevitably forces the car to a stop. If all your cells are really the same capacity then balanced would be the same at both ends. It looks like the capacity difference is as much as 6% on the 60 cells I bought.

My guess is that if you use the early numbers as gospel and don't really balance the cells (they come at about half charged) what you end up with is the weak cells get cooked on charge. And the weak cells can get bricked on an over discharge when they reverse. Thats why the numbers have changed over the years. All three brands you mention will be fully charged if you charge to anything above 3.45 volts and wait for the current to taper off. At 3.45 volts you would have to wait until the current drops to zero. At 4 volts you would probably want to stop when the current reduced to C/5. At 3.6 volts C/20 is the number most commonly seen. At 3.5 volts you could stop at C/100. Will there be differences in the state of charge with these different strategies? Yes, but they are fractions of a percent. It really doesn't matter. In the car you are talking about differences in range of a few thousand feet at most. I have read that the electrolyte used starts to break down at around 4.2v so you really don't want to get close to that. When it breaks down you get pressure build up and eventually the vent will pop and you have a mess to clean up. If you keep charging after that the cell will melt down and worse things can happen.

In China the people who write those datasheets are not the engineers who work with the batteries. There is a huge disconnect between marketing/sales and manufacturing and another disconnect between manufacturing and engineering. An example of this is all the datasheets list a self discharge of less than 3% and this is true. 0% is less than 3%. Someone looking at the cells probably asked for a self discharge figure and this is the number that got made up. It sounds good when you compare to Lead Acid, NiCd or NiMH. The other trading companies also included that on their data sheets even though it is a stupid number. You should treat the datasheets as guidelines more than anything. Be conservative and your batteries can last for many many years. Stop charging at 3.6 volts and C/20. Stop discharging at a 1C rate when you reach 2.5 volts. Consider that to be the 100% discharge point. Since you probably want your expensive batteries to last you never want to come close to that on discharge and since the voltage doesn't mean much unless you let the cells rest a few minutes to a few hours at zero current you need to count the amp hours so you know when to stop at that magic 80% point.

Best Wishes!


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