Tenergy Centura tardy termination - dangerous?

Rexlion · 2019-06-07T20:34:02.000Z

About 16-17 months ago I bought a couple dozen Tenergy Centura LSD AA cells (6 packs of 4 cells), sold by Tenergy Corporation and fulfilled by Amazon. I broke open two of the packs right away and put them on the Maha Powerex C9000 charger to top them off. All seemed fine and they didn’t take much charge (I forget how much) except for one cell that got really warm and took maybe 2600 mA before terminating. That was weird. A few months later I opened another pack and, again, one cell took a whale of a charge. When recharging these cells (mixed around, not paying attention to the specific ones) every so often I’d have a late terminator again.

Fast forward to 2 weeks ago. I opened another pack and put them on the C9000. ALL of them got really hot and took anywhere from 3400 to 3800 mA of charge before termination! I thought, whoa, is my charger acting up? So I opened pack #5 and popped them into my Gyrfalcon All-44; it doesn’t give a mA readout, but again all 4 cells were still charging after 2 hours and were really hot! I unplugged the charger to let them all cool. They weren’t so hot that I would have burned myself, but they were uncomfortable to handle.

I wrote to Tenergy a week ago and they never responded, so the heck with them. I wasn’t looking for any warranty help, I just wanted to know what they thought. Are these cells safe? Dangerous? Or what? And do they think that Amazon may have mixed in some fakes and sent them to me? (If they are fakes, they’re very good looking ones to my eye.) But I guess they don’t care. I still have one pack sealed up, if they’d wanted to inspect them. I’m pretty sure my future purchases will be Eneloops, and from a more reliable store.

So anyway, I’m posing the question to you folks: should I throw these puppies away or is it safe to keep using and abusing them?

BlueSwordM · 2019-06-07T21:10:34.000Z

Wait, 3,4-3,8A? That is absolutely insane.

Without active cooling, that is not such a good idea.

I have the impression it’s not the cell’s problem, but rather a problem with the charger.

Does charging at 1A present the same behavior?

Firelight2 · 2019-06-07T21:48:56.000Z

“Tenergy Centura tardy termination”

This sounds like one of those tongue twisters you’re supposed to say five times fast.

Rexlion · 2019-06-07T23:43:09.000Z

Surprisingly, Tenergy finally emailed a reply just before 5 pm today. Here it is:

Thank you for contacting us, we apologize for the late reply.

We do not ship or sell fake batteries, but we are unsure about the charger that you are using so cannot speak for how they charge.

However it is normal for batteries to get hot once they are close to fully charged

If you have any other questions please do not hesitate to contact us.

Interesting……

Rexlion · 2019-06-08T00:01:44.000Z

BlueSwordM:

Wait, 3,4-3,8A? That is absolutely insane.

Without active cooling, that is not such a good idea.

I have the impression it’s not the cell’s problem, but rather a problem with the charger.

Does charging at 1A present the same behavior?

The default charge rate is 1A. So, yes.

I just now put 4 AA NiMH cells in to charge: 1 Eneloop, 2 Eneloop Pro, 1 (very old) Rayovac 4.0 and will see if the charges terminate appropriately.

Rexlion · 2019-06-08T00:50:10.000Z

Ok, so those 4 cells all terminated just fine. They’d been sitting, mixed, in my drawer and some were used more recently than others, so accepted charges ranged from a low of 111mA (done in 7 minutes) to 561mA (37 minutes). They became slightly warm to the touch, that’s all.

Now I have opened my last sealed 4-pack of Tenergy Centuras. Testing with my Fluke meter showed voltages for all 4 were a hair under 1.26V. I have placed them in the C9000 for a discharge at 0.5A rate to see what they have left in ‘em after sitting in the package for close to a year and a half (maybe more, if they lingered in Amazon’s warehouse for very long). After seeing their remaining capacity I’ll decide whether to put them through a ’refresh and analyze’ cycle or a ‘break-in’ cycle (the latter charges at 0.1C for 16 hours, discharges at 0.2C, then charges again at 0.1C).

Rexlion · 2019-06-08T02:04:10.000Z

Well, this isn’t encouraging. All 4 had remaining charges that were very low for alleged ‘low self discharge’ cells: 483, 514, 492, and 503 mA respectively. I’d have expected about double that. Tenergy claims 85% retention after 1 year of storage. Unless they were shipped only half-charged to begin with? But Tenergy also claims, “READY TO USE - All batteries are pre-charged and ready to use out of the package.”

So now I’m going to do the break-in cycle on the C9000. It will take a couple of days to complete. In the process I’ll get a capacity figure when the cells discharge. When that is finished, I can do a quick discharge at 0.5A and normal recharge at 1A, and observe their behavior.

Since my other cells terminated normally and never got hot at all (merely lukewarm), I doubt my charger is malfunctioning.

Rexlion · 2019-06-10T01:25:45.000Z

The forming charge-discharge-recharge cycle yielded capacity numbers in the 1710-1800mAH range. The subsequent discharge was carried out at 700mAH rate and the capacities came up another 30 to 50 mAH each, (1799, 1833, 1759, 1822) which seems normal. These cells are rated for 2000mAH but they’re known to be overrated on capacity. I’m now doing a standard 1000mAH charge and will monitor to see if I still get excess heat or late termination.

Rexlion · 2019-06-10T04:22:50.000Z

Ok, some data here. 3 of the 4 Tenergy Centuras have terminated in a normal fashion. Each one took 13% to 16% higher input than their last discharged capacity, and this is completely normal because some energy is lost to heat. But the cell in bay #3 has taken 2678mAH so far and has not quit charging! Still chugging along.

Heat from these cells was more than my other brands. Maybe the Centuras have a higher internal resistance, or something. They get uncomfortable to hold (a brief touch is not bad) while charging, whereas the Eneloops only felt lukewarm.

Edit: the cell must have terminated moments after I looked in on it; final termination reading is 2678mAH. This cell was the one which held the lowest capacity upon discharge (1759), so it took 52% extra juice to achieve termination.
Maybe I should throw this one away; what do you all think? Questions? Comments? Curse words?

Rexlion · 2019-06-11T02:24:57.000Z

Doing some reading, I found that another member had a similar experience with his Tenergys in 2016:
how crazy is this
There seems to be something screwy about the way they take their charge.