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Battery Voltage drop
#1
Hi guys, I'm new to this forum!
Because I know that this is a good place to ask questions and learn new things, I just wanted to ask, which Voltage drop is acceptable. For example I've some cells here that I tested a few weeks ago for capacity and resistance (some of them were 0V and recovered) and exactly the 0V cells were fully charged but most of those 0V cells dropped down to about 4.04V. Is this good/acceptable? Can anyone link to a post which has some kind of spreadsheet/explanation about Voltage droprate or so?
Thanks!
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#2
I would say max drop from 4.2 to 4.1 ish within 2-4 weeks.
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#3
Hi, my first post. Yes, another dreamer here, bit by the battery bug.

I've been struggling with the same question. How much V drop is too much ?

Background:
I have a random li-ion charger, for a video ghimbal's batteries, dont' know the specs on it exactly.
I recovered some 18650 batteries from some 970 Sony style packs.

I charged the batteries: the final voltage was 4.1V

A week or so after readings:
some <2V - obviously crap.
some 3.63V, still crap.

but some only 4.02-4.04V
Is 4.02 too much of a drop from 4.1V?
Should I bother using them in a project ?
The target is a 4s5p packs.

I don't have yet a capacity tester, or any other fancy charging station.

Thank you !
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#4
Li-Ions should really drop below 4.1V after full charge. If they do, they are getting pretty old or were heavily abused.

Sub-4.1V cells could be useful in non-critical applications. Like a flash light(torch), toys, etc. I wouldn't use them in anything that requires storing them for a period of time and expect them to be functional when needed, or as a backup power supply.
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#5
(04-10-2020, 07:20 PM)SolderSoldier Wrote: I charged the batteries: the final voltage was 4.1V

If all the voltages right after charging were 4.1V, you have either a badly calibrated charger or badly calibrated tester.  Many cheap testers are.

As daromer said: To get a better picture, best to wait at least 2 weeks and allow a greater drop (say 0.1V).  You want to differenciate between initial drop in the first hours~days (not bad) and continuous self discharge all the time (bad, dying cell).
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#6
any cells that were at zero, those I would not use in a pack. If they were around 2 volts then maybe you can use them as long as they don't drop too much voltage example from 4.20 it drops to 4.18, any more then that I put the cell aside.

I encounter too many packs that I build that had balancing problems, thats why I avoid any cells that drop too much voltage. It's too much trouble to take a pack apart to look for a bad cell. If you have alot of cells only choose the best, if you have doubts about a cell, set it aside. They can be used in a flashlight.

I recently bought an IR tester (yr1030) , I test every cell with. I already found some cells that had high resistance but checked good elsewhere. I don't use those cells, its not worth it. I paid 57 dollars for the tester, but for me it was worth it. Anything that can help you weed out the bad cells is useful. And this tester is quick, you can test the cells as you get them, those that have high resistance, you don't have to waste time doing a capacity check on them. The opus can check resistance but it gives you different readings all over the place on the same cell.

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#7
(04-10-2020, 07:20 PM)SolderSoldier Wrote: I don't have yet a capacity tester, or any other fancy charging station.
I am using this charger/tester all the time:
https://www.amazon.de/dp/B074GZ5MRZ/ref=...KEbXRY31HF
I think it's a good one!

(04-10-2020, 07:53 PM)Korishan Wrote: Sub-4.1V cells could be useful in non-critical applications. Like a flash light(torch), toys, etc. I wouldn't use them in anything that requires storing them for a period of time and expect them to be functional when needed, or as a backup power supply.

Fine for me because I'm mostly going to use them in fun projects/non-critical applications!

Thanks for the help!
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#8
(04-10-2020, 10:41 PM)jonyjoe505 Wrote: any cells that were at zero, those I would not use in a pack. If they were around 2 volts then maybe you can use them as long as they don't drop too much voltage example from 4.20 it drops to 4.18, any more then that I put the cell aside.

I encounter too many packs that I build that had balancing problems, thats why I avoid any cells that drop too much voltage. It's too much trouble to take a pack apart to look for a bad cell. If you have alot of cells only choose the best, if you have doubts about a cell, set it aside. They can be used in a flashlight.

I recently bought an IR tester (yr1030) , I test every cell with. I already found some cells that had high resistance but checked good elsewhere. I don't use those cells, its not worth it. I paid 57 dollars for the tester, but for me it was worth it. Anything that can help you weed out the bad cells is useful. And this tester is quick, you can test the cells as you get them, those that have high resistance, you don't have to waste time doing a capacity check on them. The opus can check resistance but it gives you different readings all over the place on the same cell.

Beware if you do decide to use those IR testers. The resistance between the probes and cell is going to mess with your measurements. I bought one of those awhile ago and created a custom Cell holder using magnets so I could get more reliable readings.
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#9
(04-11-2020, 12:49 PM)JG27 Wrote: I am using this charger/tester all the time:
https://www.amazon.de/dp/B074GZ5MRZ/ref=...KEbXRY31HF
I think it's a good one!


Thank you JG27. It's not the first time someone recommends this charger / tester.

Thank you everyone.

As a newbie I am lacking the confidence,  but I also may be grasping at straws with the few cells I have played around.
I can't wait for this pandemic to be over so I can put some money in this new hobby.
Right now, I am counting my pennies. Selling the chairs from under me to the highest bidder lol.

All the best.
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#10
If you want a chart, ask Wolf, he's probably got some good data on that!

Here's my opinion, if you are interested:
1) Any cell that is 0.1V or less when liberated from its pack is a waste of time. It's permanently damaged. I don't have good data on it, but it's just not worth it.
2) Cells between 0.1V and 1V are almost always permanently damaged. If a cell is at like 0.85V, I might give it a chance, sometimes I get surprised. I do try to avoid them, though.
3) Now as far as voltage drop goes, you have to be precise. If you are using more than 1 charger/discharger/tester or even different slots in the same charger/discharger/tester, not all cells will be "full" at the same voltage. And your cutoff current will make a big difference, too, whether it is 100mA, 50mA, 20mA, or whatever. I usually charge to full on 1 charger, and mark the voltage of the cell 12-24 hours after the cell is charged to get a baseline voltage. I then go back 30 days later and test the voltage with the same meter that I used 30 days earlier. For me, if it's more than 0.05V lower, I put it in a second 30 day waiting period and test voltage again. The second time, if the voltage dropped more than 0.02V, I discard it as a self-discharger. Self-dischargers are bad, regardless if you are going 2P or 1000P.
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Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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