Nitecore UM2 cooked my old AA nimh as a li-on battery?

You probably just missed a termination, in that the charger failed to manage the voltage/temperature.

I’m guessing that it’s the older battery’s fault.

Chris

Older batteries with high resistance can go from a low voltage to an apparently high voltage quite rapidly. It’s a possible glitch/artifact of the charging process. The ‘smart charger’ isn’t THAT smart. It can’t actually tell LiOn from NiMh. It works on voltage.
Maybe the voltage shot up too fast, the charger thought it was lithium, and set to work on a false assumption.

BTW - those were never very good NiMh batteries, and 8 years has absolutely done them no good. It’s probably prudent to recycle the lot of them. I’ve got some OLD Annesman that are like that and I have to watch them very carefully. They WILL miss termination and put 5000mA+ into a battery designed for half that.

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That doesn’t only apply to your charger.

I have a few very old Eneloops (circa 2006-2007) that have very high resistance — they will still work on very low drain devices (probably not more than 100mA or 150mA devices) or flashlights in the Low mode only.

I keep these (my very first Eneloops) around for testing chargers nowadays, not really use them for anything else.

I’ve noted that on several chargers, either the charger refuse to charge it, or on some chargers, it will not properly detect (or will jump to Li-Ion setting).

In particular I think that happens on the Xtar VC2S and VC4S, which shows probably the same behavior as your UM2. The chargers will detect these old batteries as NiMh, then later when it’s trying to charge, detects as Li-Ion (as displayed on the charger) and sometimes goes back & forth between NiMh & Li-Ion setting (I removed the battery after observing the behavior, so I’m not sure if it really charge the battery or not).

I notice that the Miboxer C8 will properly charge this battery (but takes a very long time, as it uses the lowest charge current of 0.10A).

My SkyRC MC3000 used to be able to charge these batteries at a low charge current, but right now, even if I select low charge current, the MC3000 will show “connection break” error message after awhile of charging these batteries. The IR reading (on the MC3000) for these old Eneloops is more than 2000mOhms already.

I had same happen to me a few weeks ago.

Charging a pair of fairly old, standard NiMh AA, energiser cells (silver wrapper with green writing), one charged fine, I caught the other a while later, with many more mAh recorded more than the first and/or the capacity of the cell (I can’t remember, but it would have been around double or more to shock me like it did)… Cell was extremely hot to touch and wrap was blistering.

Must say, as I’ve not had the UM2 long, I’m pretty annoyed… I don’t get why everyone is blaming the cells, I’ve charged these many times with Zanflare C4, Nitecore D2, and other multi-chemistry chargers without issue, yes I’m sure high internal resistance makes it difficult, but Nirecore consider themselves a premium brand, and should be capable of making a safe charger…

Do these things not have temp protection in them or what? Shame HJK rates it fairly well on his comparison site if it has such massive problems…

Edit to add: I didn’t actually see if the display had switched from NiMh to Li-ion, I pulled the cell and unplugged the charger extremely quickly as I was very concerned.

500mA is only .2C and that might just be a little low to trigger any termination, but I can’t say for sure.

Chris

So wait I’m curious now. What if i put in a brand new AA nimh eneloop inside the charger that is already 90% charged… will the charger notice the voltage rise too fast and think it is a Lio-Ion as well or am i misunderstanding this?

First of all, I’m no EE, but a well implemented charging circuit is different for NiMH and Li-ion batteries/cells. They have different charging protocols, even though your charger does both.

For NiMH, ideally it’s dV/dT, voltage and temperature and for li-ions, it CC/CV, constant current, constant voltage.

They act independently depending on the voltage of the battery/cell being inserted.

Try starting with a fresh set of Eneloop/Fujitsu set of batteries, discharge them down to say…1.20v and then charging them back up and measuring the elapsed time.

Chris

I never liked those multi chemistry chargers that recognize the cell chemistry automatically. I always felt that there is possibility for something like this to happen.
Before I got a MC3000, I used my very old MAHA C9000 for NiMH and a separate charger for LiIon only.

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I agree, two different chargers is ideal.

Not while travelling….!

That said, I do have a bunch of chargers, go-to at home is the Zanflare C4 for both NiMh and Liion, I live in a small house so all my gear packed into cupboards, accessing two seperate chargers is a PITA.

Currently travelling for work, I’ve got the Nitecore with me, I’ve only got a couple of NiMh cells to charge, I’ll do them on my desk while I work so I can watch them like a hawk…

Vapcell U2 arrived shortly before I left, I didn’t have a chance to fully test it, so I couldn’t justify bringing it with me.

For traveling, I use a Panasonic BQ-CC16 for NiMH and Xtar VC2S for LiIon. The combined volume and weight of the two is less than that of a MAHA C9000 or many 4 bay universal chargers.

I travel also. And when I do I take extra batteries with me. Its a lot easier than bringing a charger.

I’m not saying my solution is best, I only want to travel with one charger… I don’t want to carry additional weight or bulk… Charger advertised as doing both NiMh and Liion, so it’s not unreasonable to expect it to perform as advertised… :question:

As above, whatever works for you; logic for this trip: I’m out for 8 weeks, hard to predict my useage, I may only charge once, may charge 10 times… impossible to budget for that kind of use for carrying spare cells…

Plus, I hate going through airports as it is, I don’t need to be pulled aside and questioned why I’m carrying a bunch of extra liion cells…

I agree with you 100 %, these things should work as advertised and expected. Unfortunately, this is not always the case, and your case is not the first one I hear of. That is why I decided to play it safe and use two separate chargers.
The only charger I trust with multichemistry duties is SkyRC MC3000, but there, you select the chemistry manually during programming, and it’s way to bulky for traveling…

One charger for both can absolutely positively work as long as you don’t do foolish things like use dead batteries from old laptops or 10+ year old eneloops. If you are using batteries less then 5 year old, you should have no problem whatsoever.

That’s also true, but the manufacturers should state it clearly in their literature or implement safety features that wouldn’t allow such things to happen, no matter what.

Yeah but those Varta batteries worked fine whenever i used them… I mean 12$ for a smart charger is a great deal but still I’m kind of worried now. I thought smart chargers could be ‘charge and forget’ for family members but i guess it is not so.

I disagree. Manufacturers can’t prevent people from being stupid.

How is the fact that I used older batteries that still worked in my devices stupid? :person_facepalming:

At 8 years old and with batteries of questionable origin, they’re most probably toast.

Just because you can fire up a light on the lower modes, doesn’t mean the batteries are healthy.

Put a 1A drain on them, which isn’t much these days and time how long the light stays on.

Chris