So I have read extensively on the dangers of reviving lithium ion batteries with voltages lower than around 2.5v (chemistry changes, crystal growth, pooching the jelly roll barriers, spontaneous self immolation, death, and destruction). My understanding is that the danger exists when a battery has been repeatedly discharged below the manufacturer's spec minimum and that batteries that fall below that threshold only once are generally not a danger if otherwise treated nicely. This would be why NOS laptop packs with lower voltages seem to be accepted as OK as long as the cells function normally.
The reason I bring this up is I'm trying to decide weather or not to trash some high drain LG batteries I salvaged from a Ryobi battery pack. These cells were all right at 0.45v but as an experiment (outdoors on cement) I decided to try gently charging them and then testing their post-charge characteristics. All 5 batteries took a charge to 4.2v and held that for 2 days. I then tried some amp measurements on some direct drive lights to get a look at internal resistance. They gave 5 amps even to and XM-L2 and 8.5 amps to an XP-G2 triple. Guess they have low internal resistance. I next put one in a 502b with 1.04 amp linear driver and timed it to the low voltage warning and got 70 minutes or about 1250 mah. Original capacity was 1300mah.
The burning questions I have are:
Is it most likely that these batteries were only discharged below 2.5v once in their existence? I don't know enough about tool pack chargers to know when a charger will reject the pack.
How do the dire warnings as outlined above apply to IMR or IMR hybrid cells? Is it only ICR chemistry that can make time bombs?
Will an IMR vent with flame even if the jelly roll layers become compromised?
Should I quit being so desperately cheap and just buy a set of 20R cells from Richard and be done with it?
The “death and destruction” part is the most scary. i have a few cells that were discharged to close to 2.5 volts and they recovered with no problems and still work, but a few that i had they fell to 2 volts or less went to the battery recycle box.
The 2.5v limit seems to include a significant safety margin. Battery University talks about the limit being below a cell voltage 1.5v for a week or more.
I suspect that 0.45v has gone far beyond any safety margin. The risk is that the metallic copper shunts have already formed and all thats needed is a bit of stress, or a shock to form a short circuit and thermal runaway.
Its not an exact science. Well OK, the fact it occurs is, but any predictability is not.
The wise move is not to play with a cell that has been subject to any condition outside the specs for proper care. Sure you can ignore or fudge those figures, sure many are fine, that does not make it wise. Its not the ones that are fine you should be concerned about, its the one that is not fine that you need worry about and the thing is it does its nasty thing without warning. All you have is indicators based on its treatment and out of spec readings. Being below a certain voltage, is the sign this cell has the POTENTIAL for bad things moreso than one that is treated well.
Its not like fuel mileage. Probably unwise to try to make a fine art of pushing the limits.
If the low voltage is from extended storage and self-discharge, especially with 'new' (old, but never used) it's no problem. If they are run down that low under a load, it's different.
I guess I don't know enough about tool packs to know if the cells self discharged or were discharged by current demand from the internal circuitry. Any thoughts?
I know you are struggling with trying to understand, but what if you think you did understand. Should you trust your understanding? Would you be safe in your understanding?
I have come across a pack just like yours, a Ryobi with LG cells, brand new in the recycle bin. The one on the left.
Written on each cell is the voltage of each cell when I first opened the pack.
0.52V
0.52V
1.15V
1.10V
1.55V
The problem is, The Ryobi charger I have for that pack charges that pack right up, no complaints. Pack runs great, doesn’t self discharge and has 1300 mAh, just like a new one.
I discharged the pack to 3.00V per cell last Spring and kept it out in the shed all summer. Just checked on it and it still sits at just under 3V. But I don’t TRUST it. Here is why.
Also last Spring I came across a brand new Makita pack that had 5 Sony cells all discharged to a very low voltage, maybe about 0.5V They too charged right up and seemed to hold their charge. Had their original capacity too, 1500mAh. I put 3 of them in my 3 cell, 3 XM-L FandyFire Warrior. Great ouput and runtime. I did several charge, discharge cycles this way and they performed great. I put those cells aside and forgot about them for a couple of weeks. 2 weeks later when I looked at them, I at first didn’t recognize them. 3 cells which 2 weeks ago looked pristine and brand new were all corroded and damp. They were also dead! During those 2 weeks after several successful charge - discharge cycles they had leaked and self discharged. I was lucky it was a slow self discharge, not a fast one. That could have been catastrophic! It was then that I realized that just because a cell charges up, or doesn’t have reduced capacity doesn’t mean it is undamaged or safe. It seems that at first they can appear to be OK, BUT after several heavy use cycles, the damage that has already occurred is made manifest.
You did the right thing in disposing of those cells.
Good information. If some of the Ryobi chargers will accept a pack with over-discharged cells I suppose technically no used Ryobi pack can really be trusted. After all, even if we open a pack and find one or two dead cells along with others with acceptable voltages we just don't know if that pack has been abused by the charger. Furthermore, it seems like these Ryobi packs may be subject to some form of internal energy demand as I have found other Ryobi packs with rather evenly over-discharged cells. Pity, those LG cells are the best I have found (free) for high drain application though the Sony 18650v is no slouch. For what it's worth I tried my pack on a charger before opening it and it was rejected.
KYFG, spoke with you yesterday about tool pack IMR cells in PM, didn’t see this till now.
I would like to add a note specifically about Roybi packs using the green LG’s, very very rarely do I find good ones of those, I don’t know of some programmer at ryobi isn’t smart enough to make the protection work correct or what, infact only about 10% of the ones I open do I keep (sell), reason being they almost always charge right back up, the ONLY ones I keep, regardless what the voltages are coming out are packs with a physically bad cell that shuts it down (and with the rest of the cells still >3v). It’s just not worth it, I’m sure the LG’s are good cells but the ryobi charger / protection circuits can not safely take care of them unless there is a total failure condition to trigger a shut down.
I still grab them when I see ’em but when I get home and am counting the packs trying to guesstimate how many good cells I’ll get, I never even count them. I wonder of ryobi packs could be charged on a different brand charger / even a hobby charger more safely.
What I have come to realize though, is that both the Ryobi and Ridgid packs do not balance charge. I am describing the 18V packs. Those packs have 5 cells in series and if one is a little lower at the start of a charge, it will still be a little low after the pack is charged up.
From what I can tell, there are circuits on the packs that monitor each cells voltage. When the pack is charging up, as soon a any cell reaches 4.20V (actually it seems like 4.25V during the charge) all charging stops. All the other cells remain at whatever voltages they were at the point the charging stops. It’s not like there are different amounts of current going to each of the 5 cells until they all reach 4.20V.
Also as the pack is discharged, as soon as ANY one of the 5 cells falls to about 2.70V, the pack shuts down.
Because of this, a pack, after a number of charge - discharge cycles, can become greatly unbalanced and loose a lot of capacity because a cell that lags the others never becomes fully charged and shuts the entire pack down early. I find some perfectly good packs that are discarded because the pack has lost capacity and the owner recycled it. All the pack needed was to have it’s weakest cell charged up independently. Of course that means opening the pack up and using jumpers to charge the weakest cell with a 3rd party charger, in my case the OPUS.
I have monitored this behavior while charging and discharging packs and measuring the voltage of each cell during the process. I only have chargers for the Ryobi and the Ridgid, so I don’t know how others act. I do know that until recently Makita packs didn’t even have a way to monitor individual cell voltages. There has been some talk that the Sony cells that are used, self balance and are able to burn off a little extra charge like NiCads can. I don’t know if I can believe that, but I don’t know how else those packs can be charged otherwise.
