First of all i would like to say i am aware of all the dangers in using old li-ion batteries with high internal resistance and i use proper protection when doing anything with them.
So the other day i opened an old laptop battery that i didnt need and salvaged the cells. All were at 0V (again, i know this is a big no-no ). Because i was curious about them, i slowly got them back to life and fully charged them. And then again, because i was curious, i put them into my test bench for capacity. And to my surprise, at 1A discharge they had over 2500mAh in them, all 6 of them. I found it amazing because to my experience, most of the cells i salvaged from old batteries were under 1000mAh. So i said, let’s see how they do with high amp test. 2.5A draw and all 6 cells only gave around 1000mAh (for comparison, my good cells give me similar result at 1A and 2.5A). The only explanation i found was that this were old cells and had very high internal resistance. Since i limit my battery testing to 2.8V and the test stops when this value is reached, i think because of high IR the cells hit that 2.8V quicker, even when they had lots of juice in them and the test stopped.
So i was wondering. Did anyone ever try anything to lower the internal resistance (knowing how dangerous this cells are) and if so, how did they do it ? I remember in old NiCd times, we would sometimes zap the cells to bring them back to life (even if this only worked short time, it was still fun thing to do). I can’t imagine myself zapping Li-ions (and i hope no one ever does it). But … is there a way to lower the internal resistance ?
I had always heard battery experts say that a li-ion cell that reads below 2.0v was toast, just throw it away.
Me and a few others here ended up doing a little experiment where we found that, that statement just is simply not true.
You can read the entire thread or just skip through it. But several of us were seeing what most would have considered a trash it cell voltage and once charged up performed as if they just rolled of the assembly line. I did do a few dated capacity test at the end of that thread. I think the cells health depends more on the number of times its been cycled and how it was cycled with the temperature it has seen also thrown in.
This is the thread FYI - some 'new' Fujitsu laptop batteries
I dont think I have ever seen or heard of a li-ion cell lowering internal resistance from cycling or any other method. As far as I know once its deteriorated its deteriorated.
First of all you didn't say what cells they are. Knowing which cell model number and brand helps to know their manufacturer rated capacity and other specifications, and so we have a capacity loss reference.
If they have dwelled for some time at 0V or close, internal damage is to be expected according to what li-ion experts say. I also heard a horror story from someone re-charging an old NCR18650B cell at fast rate and it blowing :facepalm: up, so take care.
I don't think you will be able to restore their high internal resistance problem, at least not unless you have some matter transmuting super powers LoL. 2500+mAh at 1A and then ≈1000mAh at 2.5A sounds very bad.
Personally I would likely dump those cells but, if you want to do some further testing, charge all of them to some non-harmful, relaxed reference voltage (something below 3.95V, for example), after a little while of resting time measure and note down their no-load resting voltage carefully, preferably with mV accuracy, and observe their self-discharge over a period of a few weeks, taking notes if necessary. In my experience cells in optimal condition show no perceptible self-discharge, or barely barely. This is a good battery health condition benchmark.
I have the same experience as moderator007. I have used many of those cells and they work fine for my projects, they hold the charge well over time. What i did notice though is that in time, they lose some capacity. For instance, if i salvaged the cells and tested them and got 2500mAh, it is not unusual if the same cells, after about 10-15 recharges only held 1500mAh. This mostly happens at 2.5A draw. At 1A draw they remain more or less the same. So again, internal resistance.
It also makes me wonder what the hell happens in the battery pack. For instance i found some batteries that are very very old, and they still have that 2V or 3V. And the cells could have been laying in the drawer for many years. Then i see some cells from almost new laptop and all cells are at 0V. Interesting
I read a bit of the other post and i saw them mention sometimes you need to charge/discharge cells a few times to get to the max capacity. I tested a lot of cells and always hoped for that but never actualy were able to improve capacity. I still do like 3-4 testing charge/discharge on each cells just for being sure but yeah, with me, capacity always stays the same as it did after first charge and testing.
). Because i was curious about them, i slowly got them back to life and fully charged them. And then again, because i was curious, i put them into my test bench for capacity. And to my surprise, at 1A discharge they had over 2500mAh in them, all 6 of them. I found it amazing because to my experience, most of the cells i salvaged from old batteries were under 1000mAh. So i said, let’s see how they do with high amp test. 2.5A draw and all 6 cells only gave around 1000mAh (for comparison, my good cells give me similar result at 1A and 2.5A). The only explanation i found was that this were old cells and had very high internal resistance. Since i limit my battery testing to 2.8V and the test stops when this value is reached, i think because of high IR the cells hit that 2.8V quicker, even when they had lots of juice in them and the test stopped.