Basic guidelines for when a battery is dead, needs recharging, etc?

[sygyzy]

Hi,

I know this information is scattered in various threads but is there a single source with quick "rule of thumbs" regarding when a battery is completely dead (ie needs to be tossed), needs to be recharged, should be refreshed, is too high a voltage (needs resting), etc ... for various chemistry types?

For example, in an email conversation with AW regarding IMR CR123 rechargeables

As a rule of thumb, a resting voltage of 3.6V means a cell is empty and recharging is needed asap.

What about for other cells like AA NiMH or 18650 or 14500 LiIons?

See? Super helpful. From now on if I measure one of his cells with 3.6V, I'll recharge it. Until recently, I thought voltage was an indication of charge or wellness of a battery. Obviously that's wrong.

Additionally, what information can I obtain from the ZTS battery tester I have on the way? If it says a cell is 50%, what does it mean? That it can only hold 50% of what it did new or that only 50% of it is charged? Can a 50% battery become 100% after charging? Can this metric be used as a way to determine when a cell needs to be tossed?

Thanks,
David

 

[Mr Happy]

Until recently, I thought voltage was an indication of charge or wellness of a battery. Obviously that's wrong.

On the contrary it's not wrong at all. Often it is exactly right.

Voltage always tells you something about the charge and wellness of a battery. With some batteries (like lithium ion) it tells you more than others, but it always tells you something.

With lithium ion, charging and discharging is always controlled by voltage. For example with a regular lithium cobalt cell like an ordinary 18650, the cell is fully charged when the voltage is 4.20 V (and the voltage must never be allowed to go higher than this), and the cell is completely discharged when the voltage is about 3.3 V, although many prefer to recharge at 3.6 V to prolong the life of the cell.

With an AA NiMH the picture is more fuzzy since different makes of cell react in different ways. However, an AA NiMH cell is always in need of recharging when the voltage is 1.20 V or less, and is likely to be fully charged if the voltage is higher than 1.40 V. For voltages in between it is harder to draw conclusions.

The ZTS will do quite well on alkalines and CR123A primaries, it will do less well on other types. With NiMH the results will be very uncertain.

 

[sygyzy]

Mr. Happy, thanks! I just copied some of what you said into my local cheatsheet. It's kind of confusing since you said conclusions can't be drawn for anything between 1.2 and 1.4. That's where my NiMH's normally sit.

What does a ZTS tell me exactly for the cells? What does it mean when it reads 80%? 50%?

 

[VidPro]

if you put your tounge on the end of a small 9V alkaline consumer cell, and you dont feel anything, its dead, if you Jump its good to go. If there is a terrible after-taste its Leaking :sick2: . You should toss them out when the device no longer functions.

those little lithium coin cells like the 2016 2025 and 2032 , read higher than 3V usually when new, and are usually mostly gone when they read below 3V, at 2.8rested they are pretty much Dead. you should toss them out when your light is dim :cool:

a li-ion is charged when it reads over 4V, and discharged pretty much all the way when it reads under 3.3V rested. you should charge them when your light goes dim :cool:. if its protected and Read 0V you should charge it, and see if it was just the protection that was clicked off, if it reads 0v and was not protected, its damaged a lot.

An alkaline battery of 1.5v variety is over 1.5v when new, pretty much gone at 1.0v rested , after rested it can go again sometimes, toss them out when your light dims :cool:, and doesnt come back after a rest.

a ZTS battery tester puts a small load on the battery and attempts to determine the voltage under a load, and a bit of general resistance of the battery, if it says 0% its probably really low, if it says 100% its probably really high, you should change the battery when the light is dim :cool:

 

[uk_caver]

Hoping this isn't too off-topic....

I'm currently fine-tuning with the software in a home-made charger/discharger, and I've been looking at some ~4Ah NiMH 18670 cells - some brand new, some well-used but still largely OK, and some that are basically dead and can only hold a few hundred mAh at best.

The new cells seem to have a little lower voltage when charged than the used ones (something like 1.4V compared to nearly 1.5V), but what surprised me most were the failed cells - even though I was measuring voltage while the charge was off, the cell voltage was getting up to more like 1.7V before the cells started to get warm and the voltage started to flatten off.
Presumably, the open-circuit voltage must relate to some chemistry going on in the cell - does that chemistry change as the cell ages (i.e. wears out) in any way that makes the voltage useful diagnostically?

 

[Mr Happy]

The new cells seem to have a little lower voltage when charged than the used ones (something like 1.4V compared to nearly 1.5V), but what surprised me most were the failed cells - even though I was measuring voltage while the charge was off, the cell voltage was getting up to more like 1.7V before the cells started to get warm and the voltage started to flatten off.
Presumably, the open-circuit voltage must relate to some chemistry going on in the cell - does that chemistry change as the cell ages (i.e. wears out) in any way that makes the voltage useful diagnostically?

I don't know. That's an interesting observation that I have not come across before.

There is inside a battery a kind of "capacitance" element; it stores charge temporarily with a short time constant. It may be that the dead cells cannot absorb the charge in their chemicals very well, so the supplied charge sort of "piles up" in the capacitance element and raises the voltage.

One way to test this hypothesis would be to take the cell off the charger at 1.7 V and then see how long it takes for the voltage to decrease to more normal levels -- e.g. seconds, minutes, hours or days?

 

[VidPro]

when on a charger a bad ni-mh cell will NOT show a visable V-drop for the "smart" computer , because the voltage keeps heading up, which in-turn destroys the battery further, from overcharge, the "resistance" of the battery is usually much higher then, the voltage flops around on the cell , its like anything can bend the cell to its will, as opposed to the battery being solid and the chemicals having a strong reaction, and a strong end of charge reaction. both in charging where the voltage rises , and in discharging where the voltage droops severly.
bad time for a "smart" charger and probably why they THEN resort to the 16hour slow charge methods for conditioning.
good time for a charger that has a MAHA high voltage termination, but tooo bad because the same charger also has a high resistance stop.

there must be a more technical way to say it, but basically is goes from being reactive and capable, to being a twizzler :D a gummy worm, from leaf spring to sagging PU-bed. a shock adsorber with no oil, umm, ummm, a vat of acid that is as only as strong as vinagar, a dried up o-ring, "Pat i will take Saggy Things for $500" "What is a dead rechargable battery". an Overheating spring that just mushes down either way you bend it, not Vibrant, Wrinkled skin , impressable, weakend, pathetic, malable, bad plates dried electrolyte, oxidation, insulated, not well connected to the reactables.

 

[SilverFox]

Hello VidPro,

there must be a more technical way to say it, but basically is goes from being reactive and capable, to being a twizzler :D a gummy worm, from leaf spring to sagging PU-bed. a shock adsorber with no oil, umm, ummm, a vat of acid that is as only as strong as vinagar, a dried up o-ring, "Pat i will take Saggy Things for $500" "What is a dead rechargable battery". an Overheating spring that just mushes down either way you bend it, not Vibrant, Wrinkled skin , impressable, weakend, pathetic, malable, bad plates dried electrolyte, oxidation, insulated, not well connected to the reactables.

I think the technical term for those cells is "CRAP..." :)

Tom

 

[uk_caver]

The battery analyser I'm making is mainly going to be used for 3-cell packs, but also for single cells (for working out which cells in a pack may be bad), and possibly for 2 or 4-cell packs, so I guess I may have to have some user interaction if I want to set upper limits for voltage, or maybe try and do something smarter, like working out a short charge/discharge combination that enables me to either work out how many cells there are, or diagnose the connected pack as damaged.

I presume if a pack is good, but just flat, I should be able to give it a short charge, and then get much of that power back out on a discharge?

I suppose I shouldn't take my dead cells for recycling just yet, since they might be handy to make up some test packs from.