Is it normal for keeppower 18650 cells to settle down to 4.16 volts? Some of these are brand new and some have been cycled maybe 10 times. They are legit cells from illumn and some maybe li-ion wholesale iirc.
I have much older cells that settle to 4.18 so I am confused a little.
Seems fine to me. Not much difference between 4.18 and 4.16. How long do you mean by settle down? A day, a week?
I charged then to 4.20 then probably didn’t check them for weeks. When I did they were all bang on 4.16 volts. I’m wondering if it’s just better on the cells to just stop charging at 4.16 volts since by the time I get around to using them they will already have dropped to 4.16 probably anyway. I keep a set in my lights and I always have 1 backup set for each light that I keep charged incase I am going to need to take an extra set with me.
I don’t know about those cells in particular but I’d say it’s pretty normal. A lot of variables here including rate of charge, actual termination of the charger, method/accuracy of testing voltage, temperature difference now and then, etc. Seems like somewhere I heard that higher humidity levels can also affect things to a very small degree. I just took a quick reading of five VTC6 cells that have been sitting for probably five or six weeks. Generally my cells come off the charger at 4.19v even though the charger tells me 4.20v, and these Sonys are always charged at 1A. They all read 4.155 to 4.161. I have some extra Sofirn 21700 and Dyson/Molicel 20700 and those seem to stay at 4.17 to 4.18. I keep checking the Dysons because they were well used in a portable vacuum before they couldn’t perform under load as well. When I first got into laptop pulls with old Sanyo and LG cells mostly, I checked those constantly every week or two for quite some time just curious how they were behaving. The better of those old used laptop cells did about the same thing although often dropping to 4.10v but there were some that would drop further when I looked at them again (those were obviously tired but still safe and performed ok in lower drain lights).
Remember that our norm of 4.2v is actually considered a significant overcharge for lithium-ion cells, but they can handle it without harm so that’s what we do. That doesn’t mean that they will stay exactly where you left them, however….and in this case you’re talking about a month. If you can and are curious, let them sit another month and see what they say then. If they continue to drop, then just be aware of that but it’s probably not of much concern unless they don’t settle out around 4v or better. If they just drop and drop then you need to be vigilant with them and be sure they are charging ok without excessive heat/resistance.
Yes. In fact you could stop at 4.0 and still have as much useful energy as charging to 4.2, plus you will extend the life of your cells.
The only reason to charge to 4.2 is if you absolutely need those extra few electrons for your application and you are willing to give up some lifetime for it,- or-
if you are selling cells and want to test and show that you got the biggest when you whip em out.
Look at a datasheet with a discharge curve to see how fast they drop from fully charged 4.2—there’s just so little energy available up at that level.
That’s an acceptable drop and resting voltage. The fact that they’re all pretty much dead on the same voltage is actually a good sign. And I also typically aim to stop at 4.05 +/- 0.05. As long as the resting voltage stays above 4V I’m happy
It is commonly said that every reduction in peak charge voltage of 0.1V doubles the cycle life of the cell. Even .05V makes a substantial difference. Because of this, 4.1V as a termination voltage is more appropriate than 4.2V for most commercial applications. Storage voltage and temperature also make a big difference in regards to longevity. Storing cells at 4.2V leads to rapid degradation, as does high storage temps. Here is an informative article.
A friend with a Tesla does not charge over 80% or below I think it was 40% unless it is absolutely necessary. Take care of it this way and it will last. When things are that expensive there is much incentive to do just that. For the few cells I have I don’t much care. Don’t leave them on the charger. Certainly never over 4.2 rarely under 3.5. Typically stored fully charged although at reasonable temperatures. If I had a lot more cells I would be thinking closer to my Tesla friend. However, would always charge to at least 4.1 before installing in my lights because I want bright when I want it;-)
Settling to 4.16V sounds quite normal. I wouldn’t be concerned.
I would consider those to be very health cells. Sound well matched, would be good for series or parallel use. All cells will settle from 4.20V, the fact that they have retained such balanced voltages over a period of weeks is a very good sign.
Thanks everyone. I will just charge to 4.16 from now on. Also, referring to your friends Tesla, I use the 40 80 rule for my cellphone. I am pretty sure Samsung recommends this and Apple recommends a 30 70 rule, but I would have to double check those. I always felt I was overcharging them, but now I will just stop at 4.16 for all my cells. I wish there was a charger where you could set the ending voltage that would be great. Then I could set at 4.16 and walk away, but still charge responsibly of course.