After over 24 hours of discharge refreshing, I now have the final results.
Cell 1
Cell 2
Cell 3
Cell 4
1.47v
1.48v
1.49v
1.49v
2571mAh
1579mAh
2555mAh
1372mAh
63mΩ
74mΩ
67mΩ
53mΩ
So, it looks like I was able to recover two cells to full capacity, which is great. I’ll be running cells 2 and 4 through another discharge refresh otherwise they’ll have to be put to use in another application as I’m sure you can’t use 4 batteries with such a variance in capacity.
I’m really surprised that there is such a spread, and that the low cells have that low of internal resistance. Something seems not right. IR is touchy in the Opus so I always use only one channel and hold the battery tightly (pinch it) when I check.
You might also check if you are getting different performance from different channels. That happens on some chargers occasionally since each is an independent circuit.
Curious… have the two bad cells been deep discharged repeatedly?… Like WAY down to ~0 V? My understanding (perhaps incorrect) is this can be very bad for them.
Near as I can tell it’s OK to discharge SINGLE NiCad cells to zero. You can then even short them and cold store them: http://users.frii.com/dlc/battery.htm
Information about NiMh is not nearly so clear. I have discharged a lot of batteries to zero v, bumped them with a dumb charger to a parallel short to another battery and charged them successfully. BUT, I tend to do this with older “junk” cells I don’t care about. I don’t subject this kind of abuse to decent cells if I can avoid it. But, when it has happened they don’t seem to recover back to full status.
I do know you don’t want to run a PACK too low. The weakest battery in the pack will go dead, the pack will continue to function, and that can cause permanent damage to the now dead cell killing it and the pack. A light with 4 batteries in it is essentially a pack and should be subject to the same forces.
So, those low cells may have been the weak ones that died first?
I agree, the spread is bizarre. I’ve taken the ‘good’ cells out of the charger and put them away, and I’ve put the two bad cells into channels 1 and 2 of the Opus for a discharge refresh. These eneloops have been used in nothing other than the TN4A and I have never drained the cells so much that the light will no longer switch on. The lowest I believe I’ve seen them is 0.99v. They’ve all been used in a very uniform way. Very odd.
I think I need to perform some more tests on this. You may be right, flydiver. It may be the channels; though I’ve not seen this behaviour from any of the other cells I have. When the refresh is done, I’ll run them completely down in the TN4A and charge them back up using my VC4 and see what it reads.
The VC4 will be a useful reference but as it is monitoring charge it’s not nearly as accurate as a discharge which is what you are getting from the Opus during a Charge/Test or Discharge/Refresh.
NiXX don’t parallel up too well, they are almost always used in series. Series packs are common in many applications (like ALL NiXX tool packs). The only problem with that is over discharge of the “pack”. See post #25.
I too have always read to NOT parallel connect NiMH. I read somewhere eons ago its because each cell interprets the other cell as a “load”, so they are always in a continual state of discharging each other and they never reach an equilibrium state with each other. I do not know if this is true or not… let others correct me.
I had 2 Ikea AA’s come out of the blister pack at 0 volts but both seemed to recover ok. After I cycled them a few times they seemed to be fine but I gave them away with a light so I don’t know how they were long term. I also have had several 1900mah Enloops discharge to 0 volts (unintentionally) but they recovered fine too.
Did you notice a decline in capacity?… thats where I read they can suffer. It was after repeated deep discharges too, although there was no specific number mentioned.
I have reverse-charged a standard Eneloop, down to about –0.1 volts. I thought I had killed it, but after a full charge, I compared it against some good Eneloops in a discharge test, and I couldn’t tell it apart. So, it appears it survived a small reverse-charge just fine. Though, perhaps it lost many future cycles; only time will tell.
I regularly deplete my Eneloops down to 0.8v or lower, so low voltage certainly doesn’t seem to harm them.
The only thing I’ve noticed that has hurt Eneloops is high temperature. I have a 2xAA Quark flashlight that runs very hot on maximum. After a few hours (in total) of hot usage, I noticed the Eneloops (which were only cycled a couple of dozen times), had lost about 10% of their capacity. This is very hot usage, kind of like “too hot to the touch” that you’d normally only get in high-powered lithium-ion lights. It’s a really poor driver in that light, that generates so much heat.
This is all based on regular Eneloops. The Eneloop Pros, that the OP is using, are much more delicate. I’m surprised they’d be damaged so easily. Like others, I suspect there’s something wrong with the charger, since it only recovered 2 of them.
Mark the batteries and try them in different slots in the charger (or a different charger). I have a feeling those big differences in results could be the slots in that charger since the IR’s are not that much different and the use history has been similar.
I took out cells 2 and 4, which were in channels 2 and 4 respectively, and put cell 2 in channel 1 and cel 4 in channel 2, and performed a discharge refresh. Here’s the results from the Opus.
Cell 2
Cell 4
1.40v
1.50v
2530mAh
1925mAh
53mΩ
71mΩ
I decided to get their voltages the next day using a multimeter and cell 2 reads 1.38v and cell 4 reads 1.43v.