@PeteHL .. here too, they don't dispose off properly the small batteries...

 

The serious challenge that arises when individuals collect a bunch of small batteries for proper disposal is that often that collection does not go the desired route, but gets dumped into the main waste flow.. So now instead of individual small amounts there is one large collection. Well-meaning but poorly advised folks possibly doing more damage.

 

…according to the article that I'm linking to, the life of the NiMH battery can fairly easily be reduced by unsophisticated charging.

https://batteryuniversity.com/article/bu-408-charging-nickel-metal-hydride

Just a point that if time is not an object you can ultraslow charge NiMH cells at .05C, which is the trickle charge rate. If the current is kept this low the cell will reconvert off-gassed electrolyte back to liquid internally and indefinitely. The charge will take a very, very long time but it won’t harm the battery even in continued indefinitely.

This may not seem useful but there is very good practical application. It is a method to recover an NiMH cell that has discharged below the threshold that a proper charger will tolerate. Such a cell will trigger an error in a modern NiMH charger but if charged in the minimalist way the voltage can be raised back up to something the proper charger will tolerate.

I have recovered quite a few cells in this fashion, which saves money and toxic waste in a landfill.

It is definitely true that any charger hoping to charge at the normal current, or at a fast charge rate (which is never good for battery longevity) must use a sophisticated circuit that can sense subtle changes in terminal voltage and/or temperature. My experience is that many of these chargers manage to miss these ambiguous indicators and can cook the cells quite badly if left in the charger.

When I depended on early NiMH chargers I used an external timer that limited the amount of time the charger could heat up the cell in the case of a misfire. Current chargers (no pun intended) have made this unnecessary thanks to very sophisticated ASICs and MCUs. The one place I still need NiMH cells is for my photographic on-camera flash units, though the next time I refresh the technology Li-Ion will replace the venerable NiMH.

As an aside, the NiMH cell was the perfect choice for electric vehicles for a variety of reasons but because there was a patent on high capacity prismatic NiMH batteries used for electric vehicles, which came under the control of the Chevron oil company, the option of NiMH in EVs was stifled. This episode suppressed EV development for quite a long time. It’s a shame.

 

Certainly it is the Cheap Junk chargers that do the damage, and while the instruction book may caution that charging must end after three hours, that normally happens only for those who use a timer for shutoff.

 

My first set of NiMH cells came with a nice looking Energizer travel charger... which overcharged them, so they didn't last long. Then I discovered the low-self-discharge "Duraloops" (Eneloops in Duracell livery) and got a Rayovac smart charger, which was better; those cells are still in use.

 

Energizer had their Ni-MH batteries made in Japan for many years then they became "low discharge for 1 year and come pre-charged" like Eneloops and maybe were made by Sanyo/Panasonic as re-branded Eneloops. Then Duracell Ni-MH batteries were also made in Japan for a few years but I have one made in Japan that says nothing about low discharge or pre-charged.

Costco have been selling cheap Duracell Ni-MH batteries that are made in China, have half the capacity as Energizer and do not last long. The new Duracell charger works well with Energizer batteries.

 

The best deal on NiMH batteries is from… wait for it… IKEA.

The LADDA 2450 is a 2450mAH cell that goes for $9.99 for four. They compare very favorably to Eneloops, and actually meet their capacity spec. To get the best price you have to buy them in the store. Whenever one of my kids is making an Ikea trip and visiting us, I have them get a couple of packs.

I use Eneloops extensively for photographic equipment and these are as good at half the price. There is a lot of speculation about whether they are rebranded Panasonics but the evidence suggests probably not. Whatever they are, they are very good and a real bargain.

I can’t tell you if their chargers are any good because I don‘t use them. The Panasonic chargers are excellent and I have half a dozen four cells from them.

 

Ikea does not say if their LADDA batteries are lead-acid, Ni-Cad, Ni-MH or rechargeable alkaline.

 

Ikea does not say if their LADDA batteries are lead-acid, Ni-Cad, Ni-MH or rechargeable alkaline.

They are NiMH.

 

The Li-ion battery if it is allowed to be discharged below 50% is damaged whereas the NiMH battery can be completed discharged without damage. So if you are assembling a Li-ion battery-powered device, you must either know how quickly the battery is being discharged or have circuitry to shut off the device before the battery becomes discharged too much. This is a serious impediment to powering your own circuit with a Li-ion battery as opposed to NiMH.

The energy density of the Li-ion battery is greater than that of NiMH, but I wonder if that factors in 50% discharge and close to full discharge of respectively Li-ion and NiMH batteries.

https://turbofuture.com/industrial/...-Hydride-NiMH-or-Lithium-Ion-Li-ion-batteries

 

The Li-ion battery if it is allowed to be discharged below 50% is damaged…

The energy density of the Li-ion battery is greater than that of NiMH, but I wonder if that factors in 50% discharge and close to full discharge of respectively Li-ion and NiMH batteries.

I find this confusing. If I have a properly rated, let’s say, 3000mAH LiPo cell, are you saying that you can only use 1500mAH of its energy? If so, that’s not right. The 3000mAH rating means it will provide 3000mAH.

What is it that you are only using 50% of?

Also, if I have two cells of the same size, one with a lithium chemistry and one with a NiMH chemistry, it is trivial to see that the lithium cell has far more energy, and so a higher energy density. I don’t see how the “50%” thing is involved here…

Can you clarify? 50% of what? If you mean \( \mathsf{\frac{4.7V} {2}} \) that’s really not relevant to the energy discussion. The cells open terminal voltage is just a characteristic of its chemistry and doesn’t tell you how much energy is present. In fact, determining SoC (State of Charge) using the voltage is pretty useless. This is why “fuel gauges” on batteries use coulomb counters. They actually watch the electron flux as it leaves the battery for the load to see the difference between the full charge (which the watch going in) and the end of discharge point as they watch it going out.

Of course, voltage is very relevant to applications. One of the shared characteristics of both lithium ion and NiMH cells is the flat discharge curve where they produce a relatively constant voltage until they suddenly collapse.

 

I use modern NiMH batteries for some things and use LiPO batteries for other things.
Here are their voltages:

 

I find this confusing. If I have a properly rated, let’s say, 3000mAH LiPo cell, are you saying that you can only use 1500mAH of its energy? If so, that’s not right. The 3000mAH rating means it will provide 3000mAH.

What is it that you are only using 50% of?

Also, if I have two cells of the same size, one with a lithium chemistry and one with a NiMH chemistry, it is trivial to see that the lithium cell has far more energy, and so a higher energy density. I don’t see how the “50%” thing is involved here…

Can you clarify? 50% of what? If you mean \( \mathsf{\frac{4.7V} {2}} \) that’s really not relevant to the energy discussion. The cells open terminal voltage is just a characteristic of its chemistry and doesn’t tell you how much energy is present. In fact, determining SoC (State of Charge) using the voltage is pretty useless. This is why “fuel gauges” on batteries use coulomb counters. They actually watch the electron flux as it leaves the battery for the load to see the difference between the full charge (which the watch going in) and the end of discharge point as they watch it going out.

Of course, voltage is very relevant to applications. One of the shared characteristics of both lithium ion and NiMH cells is the flat discharge curve where they produce a relatively constant voltage until they suddenly collapse.

I agree that the author is not being absolutely clear as to what he means by 50% discharge. But I would interpret that as meaning that if the battery is rated 1000 mA-hours, then discharging it safely means stopping its discharge after 500 mA-hours of use.

-Pete

 

No, A lithium cell is fully charged at 4.2V, is half discharged at 3.6V and must be disconnected at 3.0V.
My graph of an 800mAh lithium cell shows that it is half discharged when its voltage is 3.6V to 3.7V (also its storage and selling voltage). Half of its mAh are used-up and half of its mAh remain to be used.

If it is discharged lower than 3.0V to 3.2V then it has become damaged.
A Lithium cell also becomes damaged if it is frequently fully charged.

 

I agree that the author is not being absolutely clear as to what he means by 50% discharge. But I would interpret that as meaning that if the battery is rated 1000 mA-hours, then discharging it safely means stopping its discharge after 500 mA-hours of use.

-Pete

That’s simply not true, though. I have personally tested many lithium cells that even exceed the manufacturer’s capacity rating. A reputable 3000mAH LiIon cell will provide 3000mAH of energy. So, the idea of discharging a cell “50%” and having to be.. somehow 0%... doesn’t hold up.

 

That’s simply not true, though. I have personally tested many lithium cells that even exceed the manufacturer’s capacity rating. A reputable 3000mAH LiIon cell will provide 3000mAH of energy. So, the idea of discharging a cell “50%” and having to be.. somehow 0%... doesn’t hold up.

The article that I provided a link to in my post #30 was one of the top results in my search for characteristics of the Li-ion cell. So far, I haven't made use of this type of battery at all, so I was merely spouting what I had read. This goes to show that it is good to take a grain of salt with whatever you read on the web.

 

The article that I provided a link to in my post #30 was one of the top results in my search for characteristics of the Li-ion cell. So far, I haven't made use of this type of battery at all, so I was merely spouting what I had read. This goes to show that it is good to take a grain of salt with whatever you read on the web.

Battery University is a very reliable source for information on batteries of every sort. If they are not authoritative, they are very close. I recommend it highly.

 

A Lithium cell is 4.2V (100%) when fully charged and is 3.6V or 3.7V when half discharged (the 50% mentioned).
The remaining 50% of the charge is used when its voltage runs from the 3.6V to 3.7V down to 3.0V to 3.2V.
The graph I showed shows no charge remains (0%) when the cell voltage has dropped to 3.0V to 3.2V.