HKJ, thanks a lot for putting this down in a nice post for reference.
It was much needed. Ought to be stickied.
That would be good, and thanks for this one.
So that’s how you test charging voltage. Thanks for doing this guide, I’m getting my Fluke out right now.
Thank you!
Hi again, HKJ.
As always, thanks for your posts. They are really interesting.
Keeping in mind the information shown on this post, and the information shown on this old post, ( Charger settings ), are these sentences right?
Please confirm them for clarity sake.
1) Charging Li-ion cells to 4,1V means cells will have more lifetime, but less energy.
2) Charging Li-ion cells to 4,25V means cells will have less lifetime, but more energy.
3) Termination current high will make voltage drop after termination high.
4) Termination current low will make voltage drop after termination low.
5) Charging a cell to 4,2V with low current termination will give more performance than charging the same cell to 4,2V with high current termination.
6) The best possible charge to obtain maximum performance from a Li-ion cell is to charge it to 4,25V, and a very low termination current. (Forget about cell lifetime).
And some questions:
It is really interesting to go to 0,025A termination current, or even lower in big capacity cells (forget about charge times) or it doesn´t worth it?
Do you recomend to modify termination current setting, depending on the capacity of the cell?
For example:
5000mAh cells -> 0,125A termination current.
4000mAh cells -> 0,1A termination current.
3000mAh cells -> 0,075A termination current.
2000mAh cells -> 0,05A termination current.
1000mAh cells -> 0,025A termination current.
Again, thank you very much for your work.
Why would you want to charge to 4.25v? Are you that desperate for a tiny smidgen of performance you probably can’t even quantify without pretty good tools and knock a good percentage of your battery life off?
”
How does capacity correlate with charge voltage for lithium ion batteries?“:Charge voltage experiments with lithium ion batteries showing how capacity varies with charge voltage and higher cycle live with lower charge voltage
Thanks for the link, very useful and interesting.
Answer: to obtain maximum performance. I know doing this will cause shorter lifetime, but performance is performance.
Why drag race cars engines have this setup? For maximum performance. It doesn´t matter if it lasts for 2 or 4 miles, the most important is to perform as better as possible in the first mile and win the competition.
Answer2: don´t worry, I won´t charge my batteries to 4,25V. I preffer to extend their lifetime.
I sometimes wonder about 4.35v batteries. How much is that ACTUALLY a superior/different chemistry, and how much is ‘hot rodding’ the battery at the expense of shortening it’s life?
Hi again.
After reading SkyRC MC3000 charger manual, I have one more doubt:
(Regarding Termination, http://www.skyrc.com/index.php?route=product/product/download&download_id=149 , page 13/22 )
The termination current of the CV-phase of Li-Ion battery charging algorithm, also of NiZn. When
reaching TARGET VOLT, e.g. 4.20V, this option will hold the voltage constant while automatically
reducing the current down to the specified value before it terminates the charging routine. A high
termination current serves battery health but will not charge the full battery capacity. The
parameter defaults to 10% of C.CURRENT, an industrial standard. “Zero” means an ever
decreasing charging current: not good for your patience or battery but allows to produce quasiconstant
4.200V battery voltage if that’s what you’re after. OFF means no CV-phase once the
target voltage has been reached.
That means high termination current is good for batteries lifetime?
They are correct, I did test a bit with varying charging voltage and termination current: Battery charge voltage and current
The manufacturer do often include a termination current in the datasheet. A lower termination current will charge the cell to a higher voltage and stress it a bit more.
With smaller cells it is often necessary to reduce the termination current to get a full charge, in the hobby charger world the standard is 1/10 of the charge current.
Hi HKJ.
Thanks again for your answer.
When you say: ” A lower termination current will charge the cell to a higher voltage and stress it a bit more.” I don´t understand at all this sentence. Maybe it is wrong?
For me it is clear now that low termination current stresses the cells a little bit more than higher termination currents.
But I understood the voltage only increases during the CC phase, and would be always the same (constant voltage) when the CV phase starts. The charge intensity (amps) decreases during this CV phase. Depending on how high the termination current is, the voltage drop will be higher when the charge ends.
In fact, you say in the original post “In the CV phase the charger will hold stable 4.20 volt and the current will drop until it is down to the cutoff value.”
So… I am lost. Sorry, my english is not very good, and maybe I am not understanding you properly. I only want to understand all the theory behind this process.
Try checking the table in this article Battery charge voltage and current
Especially the charge voltage and termination current and the cell voltage after 60 minutes, then I hope you can see what I mean.
During the CV phase, the bigger the difference in voltage between cell and charger, the higher the current flow.The charger will keep pumping 4.20 volts while the cell is not at that voltage yet. If they were equal, there would be zero current flowing. That’s why charge termination current is meaningful. The higher termination current means the cell is still that much lower voltage than 4.20 volts.
Ah, OK!
I think I get it. Thank you both for the explanation.
In the table of http://lygte-info.dk/info/BatteryChargeVoltageCurrent%20UK.html seems it is better for cell performance to charge to 4.15V with termination current of 0.050A (Energy = 95), than charging to 4.20V with a termination current of 0.400A (Energy=93).
I assume this setting (4.15V, termination 0.050A) is also better for cell lifetime, right? (The only “problem” in this case will be the time you need to finish the charge of the battery).
Would it be possible to charge with 1.5A (or more) during the CC phase to 4.18V-4.19V, and then set up a termination current of 0.025A (or less) on the CV phase?
What I am trying to find is the best performance/cell lifetime/charge time ratio.
Thanks again, and sorry for so much questions!
Correct.
I cannot give a answer to that. Storing the cell at higher voltage will wear the cell down faster, but fast charging at high voltage will also wear the cell down.
Algorithms to fast charge LiIon cells uses a high current for the initial part of the charge, then reduces the current when the cell is partly charged (This has nothing to do with CC/CV charging). Research has show that high current will not reduce lifetime when the cell is at a low charge state.
Yes, the MC3000 charger can do that.
The cutoff voltage around 2.75V or 3.0V is a kind of standard for the rechargeable 3.7V battery cell, mainly determined by the IC of the protection PCB for the battery pack. As flydiver wrote: I try to keep the voltage above 3.0v at all times and generally above 3.2v. There is VERY little capacity under 3.0v and the volts drop precipitously after that making it a slippery slope. Once the cell voltage goes under 2.5 it gets dicey, below 2.0V it will cause permanent damage,can not be recharged any more.
From our long-term experience in the rechargeable battery industry, the cutoff voltage is affected largely by the discharging current as well, just as the charging cutoff, and a voltage recovery immediately after the cutting-off.
The ones I tested had considerable lower cut-off than that (In the 2.0 to 2.5V range): Discharge protection test
And the cut-off was always at exactly the same voltage, independent of current. It also makes the most sense, it would be fairly complicated to adjust the cut-off voltage depending on current drain.
Note: My test is for single cell protection, not for battery packs.
Many thanks for your details. Yes, you are right, the testing results from our engineering department are usually for the complete battery packs with protection PCB, which seems quite different from your testing results. However, all your testing about the battery cells and chargers can be a perfect reference for our customers to get a most suitable charger for their battery packs. 
Since there are so many Li-ion 18650 battery cells from difefrent cell manufacturers, that can be available for lighting systems, is it possible for you to test them for the cycling performance, or do you happen to have the cycling results for some battery cells? Thank you in advance.
Not really, doing 100 cycles takes a month and I do not have equipment to run many batteries at a time.
Yes, it’s quite a long time to complete the cycles, which is usually more than 2000cycles.