Just found a laptop battery that has been laying around my house for a few years. What should the minimum voltage for a cell be if I want to salvage the cells safely?
Generally 2.5 volts.But some have been saved at lower voltages.Read up on recovering laptop cells and proceed with caution.
I'll second that, 2.5volts, then find a way to very slowly bring the voltage back up. If it were me, I would probably try to parallel it with another charged 18650 for about 5 seconds at a time, checking the voltage each time after disconnecting it to see if the voltage was climbing. No more than 5 seconds at a time and if it did not go any higher after a few 5 second sessions I would toss the cell accordingly. An Opus BT-C3400 V.2.1 or 2.2, charger would be very helpful with this kind of situation. It can give you the internal resistance of a cell and it can charge a 18650 cell at 200ma.
Yeah, after pulling it apart and testing with a multimeter, these show no charge at all. Oh well.
Thanks!
Sorry about that, there are a lot of cheap packs on ebay that will yield you some nice 18650's. My last score turned out to be 9 Samsung 4.35volt cells that have ~3000mah each, I paid 30 for the pack, but that was only because I knew that those cells were in there and I wanted to try them out. Better throw those dead ones out.
An Opus charger will kick down to a very low charging current initially on low voltage cells no matter what you set the charge current to. As the cell voltage increases to a suitable level it will gradually start charging at the current you set it for.
If a cell is to low to charge the Opus will not charge it
The cells show zero or the pack shows zero?
The pack should have LVP that will cut the output connection when the cells get low. So zero on the pack does not necessarily mean zero at the cells. The cells will continue to drain slowly though. If the pack sat a long time, the cells may be below 2.5v. Some of us have revived cells in old, but never used stock (at our own risk). That isn't recommended for cells that have been used and may have gone too low multiple times.
Yeah, I pulled it apart and checked individual cells. Completely dead. Battery pack was sitting unused for about 5 years so I’m not too surprised.
I realize that everyone is in a different work environment, but it you start putting out feelers you might wind up with more batteries than you know what to do with. I’m the ‘recycling guy’ and ‘proper disposal nazi’ at work. So when people have electronics waste, they bring it to me and I make sure it gets recycled or disposed of correctly. Since September, I’ve broken open 8 packs and have been able to be pretty selective. I now have plenty of 18650 batteries. Especially considering that I only have an A6 and now a X6 that will take them. I still have at least three packs that I have yet to crack the plastic on. After reading some suggestions here on BLF, I even went prowling at Home Depot and Lowes in the battery recycling bins, but never found any.
This is a problem I now have. Ok, “problem”. lol. I have about 5 times as many 18650 cells as I do lights that take them. I love pulling apart old laptop batteries and reviving or using the good cells. I’ve saved plenty from 2.5v, a few that were just over 2.0v. Nothing really well below that.
Most are older Samsung or Sony cells, 1800-2200mAh after being used in a laptop for a good 7-8 years. Still lasts long enough in a light though. Plus if it dies after an hour… it’s not like I dont have 60 more 18650’s in storage.
Throwing this in this thread rather than creating a new one. I just cracked open a 9 cell HP pack that was tossed and sat unused for at least a year. I left the cells welded parallel (3) but cut the series connections. They are Samsung ICR18650-30A’s. Set#1 @ 0.76v, Set#2 @ 1.76v, Set#3 @ 2.09v. Pack dated 4/2012.
Sets#1 & #2 I’ll just recycle, but is Set#3 worth trying to revive? I have both an OPUS & a hobby charger.
-Garry
Hmm . . . no responses. So I just went ahead and connected Set #3 up to my hobby charger (remember, 3 cells in parallel) @ 100mA charge rate for 3 mins. The charger’s voltage display jumped above 2.50v within a second or two. After 3 mins I stopped charge and checked voltage with my DMM, 2.87v. I’ve now raised the charge rate to 300mA (now 100mA per cell) and intend to fully charge the pack at this rate (might take quite a while). I then expect I’ll take voltage measurements after charge is complete and then at regular intervals to see if voltage drops. After a day or two I guess I will then discharge test it for capacity. I’m wondering what rate to discharge at that will be safe yet not take forever, 2.0A sound ok?
-Garry
I would personally probably even give set #2 a go, instead of going to full charge though get them up to storage charge levels (3.7-3.8) then let them sit for a day or two and check for voltage drops, if there isn’t any they should be good to go.
As far as discharge, assuming the cells are showing good, they could technically handle up to 6A each. For their first run however I would probably do 3A for the set of 3, so 1A per cell.
Thanks for the reply!
-Garry
Well set #3 seems “worn out” & “tired” (kinda like me!). Charged it up initially at 300ma for maybe 6 hours, then next day raised charge rate to 1.5A (0.5A per cell) until full. In 3 hours time it had dropped off 0.02v. 17 hours later it was down another 0.03v. Recharged again and it took 384mAh back into it. Let it sit and about 22 hours later it had only dropped 0.01v. Then I discharge tested it at 1A and it yielded 6,108mAh (2,036 per cell). I didn’t compare voltages to “healthy cells” yet but I believe voltages are low. I think I’ll just recycle these cells 
.
-Garry