HR03 battery (NiMH AAA) reading 2.5 volts- how?

[ralphrmartin]

I just put a recently charged Eneloop HR03 battery in a circuit, which destroyed it. On checking the voltage from the battery, it is reading just short of 2.5 volts. Other recharged batteries of the same kind, charged in the same charger, read around 1.4 volts.

How can an HR03 produce such a high voltage?  Is this a one off issue? Or do I need to build protection into my circtui for such overvoltages?

[woofy]

Is the 2.5v real, or just an illusion caused by a flat battery in your multimeter.
If its real, its not something I've ever come across. Don't really see how an otherwise good charger could get it there.

[tunk]

Difficult to say until you tell what your "circuit" is.

[ralphrmartin]

The battery was pulled out of the circuit to test its voltage.I seriously doubt there was anything my circuit could do to the battery other than slowly discharge it.

I dont think the multimeter is likely to be the problem, as 3 other just-charged batteries all gave expected readings on the same meter, when tested after the dodgy battery.

The charger is supposed to detect different chemistries, and charge batteries accordingly, but its hard to imagine what it could do to a battery to almost double its voltage. Are such batteries a single cell? If not, that might allow an explanation.

Further insights welcomed! Thanks.

[bdunham7]

How much current can the battery source at 2.5V?  If it is a genuine Eneloop NiMH it is hard to imagine what would cause this.  Perhaps some weird internal mechanical failure?  If it is some sort of fake that uses an internal Li-ion battery and a converter, then it might be possible if the converter circuitry failed.

[IanB]

The charger is supposed to detect different chemistries, and charge batteries accordingly, but its hard to imagine what it could do to a battery to almost double its voltage. Are such batteries a single cell? If not, that might allow an explanation.

"Supposed" might be the operative word here. I do not know how the NiMH chemistry could possibly produce 2.5 V, but let's suppose the charger somehow charged it as if it were lithium ion instead of NiMH, the the charger could have tried to force it up to 4.2 V, and in the process of destroying the cell, it might have left a residual voltage of 2.5 V behind.

That's the only guess I could make. Because, in principle, an Eneloop should not be able to have such a high voltage.

I would never recommend to use such "multi-chemistry" chargers. I would always use an NiMH charger for NiMH, and a lithium ion charger for lithium ion.

[ralphrmartin]

I've seen fake 18650 cells full of sand, but why fake a NiMH battery with a Li-ion cell? That would not seem like a cost effective thing to do.

I'm afraid I didn't keep the bad battery to measure its current sourcing ability. I did not want to risk accidentally using it to power another circuit.

So far I have not had any problems with eneloops and my multi-chemistry charger, using them for many years, for many things. I do take the point that an unexpected condition may cause problems.

Maybe you have more bench space than I do for different chargers (a separate dedicated NiZn charger is already taking up extra space).

[IanB]

Yeah, I'm not thinking it's a fake NiMH cell, but rather, what would happen if you tried to somehow force an NiMH cell up to a very high voltage? Like, maybe it could overheat, and vent, and dry out, and then stop functioning as a cell, then hold on to a residual high voltage?

I don't know, but since you made the observation it seems it must have happened somehow?

[Rick Law]

My older LaCross BC700 NiMH (only) charger would regularly pushes AA/AAA charging voltage up to 1.9V range in the later charging stage, as least according to the charger's display.  Say there is a voltage regulator/reference not functioning properly, a charger pushing it up by another 0.5V to 2.4V is not that unimaginable.

Too bad you did not keep the "2.4V cell", it would be interesting to see if it really is 2.4V and for how long.  You should keep an eye on your charger to see if it happens again.  If it pushes one AAA to 2.4V, it may do it again on another AAA.

[radiolistener]

The charger is supposed to detect different chemistries, and charge batteries accordingly

Usually such chargers has a button which allow to select proper battery type if auto-detection is failed and selected incorrect battery type. If you didn't corrected battery type it can damage battery and even can do fire...

[ralphrmartin]

I dont see any button to force battery type.

The charger has since charged several other batteries without issues.

[radiolistener]

Usually they using single button for two functions. When you insert the battery, you have several seconds to change it's type with the button. After that the button works to select charge current.

I have that charger, but it detects battery voltage properly, so there is no need to change it after automatic detection.