This thread for is those who might be interested in the topic.

I recently started looking into Li-ion 1.5V AA rechargeable batteries as a replacement for NiMH types when I found some that had a comparable cost (frugal person that I am).
These have an internal Li-ion battery of typically about 3.7V, which is then dropped to a regulated 1.5V output by an internal buck switching regulator to be more compatible in devices that are designed for the 1.5V nominal of an alkaline primary cell as compared to the 1.2V of an NiMH.
Their Ah rating is generally comparable or slightly better than NiMH, but their Wh rating is significantly greater (close to the 3-4 Wh of alkaline) due to their higher constant-voltage output, (which may or may not be significant in use, depending upon the device being powered).
They are also rated for more lifetime charge-discharge cycles (2 to 3 times). Of course that's only really significant if the battery is used in a high power application where it frequently needs to be recharged (of which I have none).

So I ordered the ones below from amazon to try them out.

They seem rather cheap so I'm interested in seeing if they work well, or if some of the other brands cost more for a good reason.
One difference is that these batteries don't have a USB-C charge-port as many of the others do, as they use the included charging station instead, and thus don't need a multi-plug USB cable to charge more than one battery at a time.
Another possible advantage of not having that charge port is it gives a little more room for the Li-ion battery inside the package.
I suppose not having that socket in each battery would reduce the cost some, but not necessarily enough to account for the significant difference in price between brands.

A primary reason for my buying them (besides curiosity) is that I have an electronic front-door lock using four AA batteries that stops working at about a 1.2V/battery voltage since it is designed for 1.5V alkalines, thus NiMH's only last a few months (they start at slightly over 1.3V when fully charged but then drop to 1.2V well before their typical discharged voltage of about 1V).
Hopefully these Li-ion's, which maintain a constant 1.5V output until discharged, will last longer in that application (at least comparable to the alkalines).

So I'll report back here with my experience with them as I put them to use.

Cheers.

 

As previously mentioned, I have the type with a built in charger. Both types must have a buck converter from c3v to 1.5v with a cutoff around 10% SoC. Whether the charger side is a separate chip remains to be seen, I've resisted the urge to dismantle one! I learnt the hard way that the built-in charger type must be removed before charging unless its a completely isolated single cell.

 

I tried some with the charge port built-in and I found that their capacity dropped rather quickly. I will be interested in the results for these batteries.

 

I assume the charging circuit is still inside the battery, the difference is just how the 5V charging voltage is applied.

And one of my main concerns is the battery self-discharge rate as it should operate around a year in my lock based on how long alkaline cells lasted.

 

3600mWh @ 1.5V = 2400mAh. Not likely in that form factor because good 18650's are at about that capacity and they're significantly larger.

Plus, inexpensive Li-ion batteries are typically poorly constructed and present a fire hazard. A video with Adam Savage was posted at least 3 times in the past year or so.

 

3600mWh @ 1.5V = 2400mAh. Not likely in that form factor because good 18650's are at about that capacity and they're significantly larger.

Surprised you made that error.
That's for Ah but not Wh.

According to google AI:
A typical 18650 lithium-ion battery has a capacity ranging from 8.5Wh to over 13Wh.

The Wh capacity is the battery voltage times Ah and the 18650 has a nominal voltage of about 3.6V.

inexpensive Li-ion batteries are typically poorly constructed and present a fire hazard.

As far as the danger, we'll see about that also.
I could end up with a burned out electronic lock.

 

I would also be interested in your results, Carl. I also have a pair of applications where they could be used.
To me at least, an important parameter would be their self discharge rate. As you mentioned, the cells must have some sort of buck regulator, which must still continue to consume current even when the load itself is not requiring any (or minimal) power.
The micropower topologies I am familiar with, employ pulse skipping and/or frequency-lowering architectures. Nevertheless the control circuit’s own consumption is still at least an order of magnitude higher than self discharge.

 

The micropower topologies I am familiar with, employ pulse skipping and/or frequency-lowering architectures. Nevertheless the control circuit’s own consumption is still at least an order of magnitude higher than self discharge.

I would think there's a custom ASIC that both controls the charging and provides the buck converter regulation.
Hopefully it's designed so its power consumption does not significantly add to the batteries self discharge rate at light loads (but we shall see).

Edit: Below is a drawing of the battery internal control circuitry, which appears to show one IC.



The self discharge rate of a Li-ion battery is stated by google AI to be up to 3% per month, which works out to about 42µA for the 3.6V internal Li-ion battery.
For a 1 year battery life, the allowed total self-discharge and load current draw would be about 120µA from the battery.
That translates to about 150µA load current at the 1.5V output, assuming a very high-efficiency buck converter.

Below is an example low power, high efficiency buck converter that has only a 360nA quiescent current and up to 90% efficiency at a 10µA load current,
which shows it should be possible for the Li-ion buck converter to get similar efficiencies:

 

Received the Li-ion cells shown in my first post.
Using my free Harbor Freight multimeter, they all measured slightly over 1.5V after being charged.
Installed them last night in my front-door SimpliSafe electronic lock where they seem to be working fine, operating its internal motor to open and close the dead-bolt remotely, which likely takes about an ampere peak (typically these 1.5V Li-ion cells have a 2A average current rating with a peak of 3A).

Now, nothing much left to do but wait to see how long they last in this low (average) power application.

 

to be up to 3% per month

As discussed elsewhere, my measurement of various LiPo and LFP cylindrical and pouches was generally significantly better than that, 1 set showed <5% over 18mo at room temp.

 

As discussed elsewhere, my measurement of various LiPo and LFP cylindrical and pouches was generally significantly better than that, 1 set showed <5% over 18mo at room temp.

So that would indicate that the self-discharge rate of these 1.5V Li-ion batteries is likely mainly determined by the quiescent current draw of their internal buck-converter electronics.

 

Datasheet:
“high efficiency buck converter that has only a 360nA quiescent current and up to 90% efficiency at a 10µA load current,”

Me:

 

So that would indicate that the self-discharge rate of these 1.5V Li-ion batteries is likely mainly determined by the quiescent current draw of their internal buck-converter electronics.

I have used these rechargeable batteries and compared with other people statements. A rechargable battery will last much less the regular dry cell batteries. The reason is that the dry cell is a small generator of electricity. It will continue to produce power till the negative pole is completely eroded. The rechargable is more like a super capacitor: can be recharged again and again, but does not produce energy. I have one of the cheap AAA batteries soldered to a small timer and it has been working for near 10 years, still no sign of giving up.

 

I have used these rechargeable batteries and compared with other people statements. A rechargable battery will last much less the regular dry cell batteries. The reason is that the dry cell is a small generator of electricity. It will continue to produce power till the negative pole is completely eroded. The rechargable is more like a super capacitor: can be recharged again and again, but does not produce energy. I have one of the cheap AAA batteries soldered to a small timer and it has been working for near 10 years, still no sign of giving up.

True, but the point, IMHO, is that as a replacement in a long term low drain environment is not what they are suitable for. Kids toys, my radiator valves, battery shavers, etc and other medium term, high demand environments where self discharge isn't an issue but regular replacement costs are, are their preferred environment .

 

True, but the point, IMHO, is that as a replacement in a long term low drain environment is not what they are suitable for. Kids toys, my radiator valves, battery shavers, etc and other medium term, high demand environments where self discharge isn't an issue but regular replacement costs are, are their preferred environment .

Yes obviously, self discharge is the problem and it may even be the main factor for voltage drop. What I was thinking is that if there is a little room somewhere inside the door, 4 or 5 AA or even AAA batteries can keep the rechargeable ones slowly refilled via a 500Ω to 1kΩ, depending on how often the electric lock is used, can keep them going for years , while the high-current Ni-MH can provide the muscle for sudden current demands.

 

The reason is that the dry cell is a small generator of electricity. It will continue to produce power till the negative pole is completely eroded. The rechargable is more like a super capacitor: can be recharged again and again, but does not produce energy.

Not true.
They both use a chemical reaction to produce electricity.
The only difference is that the process is reversable in a rechargeable battery, but essentially not so in a primary battery, such as an alkaline or carbon-zinc.

A rechargable battery will last much less the regular dry cell batteries.

Only if self-discharge is a significant issue in its use.
The AA Li-ion types have stored energy comparable to an AA primary alkaline type, and NiMHs are not far behind

I have one of the cheap AAA batteries soldered to a small timer and it has been working for near 10 years, still no sign of giving up.

Then you have a timer that uses much less current than my analog clocks or lock, where AA alkalines last less than two years, so that observation is not really pertinent to this discussion.

Yes obviously, self discharge is the problem and it may even be the main factor for voltage drop. What I was thinking is that if there is a little room somewhere inside the door, 4 or 5 AA or even AAA batteries can keep the rechargeable ones slowly refilled via a 500Ω to 1kΩ, depending on how often the electric lock is used, can keep them going for years , while the high-current Ni-MH can provide the muscle for sudden current demands.

That would be contrary to my reasons for using rechargeable batteries in my eight clocks and the door lock.
It's to avoid the expense of buying many batteries every year, and all those dead ones ending up in a landfill.
And your solution wouldn't significantly reduce the primary batteries used by the lock (besides which, there's no room "inside the door" wherever that would be).

Thus my experiment to see if the Li-ion types will work in my door lock (where alkaline types last about a year, but I'll be satisfied if the Li-ions go for at least 6 months).
I have already determined that the low-self-discharge NiMH ones have adequate operating time in my clocks.

 

I have already determined that the low-self-discharge NiMH ones have adequate operating time in my clocks.

The clocks that you have (based on what I understood from our earlier conversation) are the "ticking" motors. The draining time in such motors is probably the same as self-discharge of the batteries you have. The "relevance" I saw in the timer thing was that you will never get a rechargeable battery live 10 years, no matter what. Even if you put it on a shelf. The electricity that they produce is 100% opposite:
1- Dry cell: You will never charge them. They come out of package producing electricity spontaneously
2- Rechargeable cell : You will never get electricity from them without charging. They do show some voltage but that is because they are charged in the factory
Anyway, good luck and I will be waiting to hear the test results.
BTW do the batteries get cold in the winter? is the front door area heated like the rest of the house?

 

The clocks that you have (based on what I understood from our earlier conversation) are the "ticking" motors. The draining time in such motors is probably the same as self-discharge of the batteries you have.

Not quite.
They take about 50 to 200µA average whereas AA alkalines typically lose about 2-3% of their capacity per year which calculates to an equivalent self-discharge current of roughly 5-7µA.
Have you never had one of those clocks and had to periodically replace their batteries?

1- Dry cell: You will never charge them. They come out of package producing electricity spontaneously
2- Rechargeable cell : You will never get electricity from them without charging. They do show some voltage but that is because they are charged in the factory

True.
But how is the relevant to this thread?

do the batteries get cold in the winter? is the front door area heated like the rest of the house?

They do not get cold.
The lock mechanism and batteries are located on the inside of the door.
The only thing outside is a small, wireless keypad with its own battery.

 

I bought a set of 4 of these with charger, around 18months ago, specifically to replace radiator iTRV AA batteries.

One failed after a few weeks. Completely dead.
Re-charged it, failed again after a couple of weeks.
Supplier replaced it free of charge.

A second one failed sometime later, so I decided to abandon the idea of replacing all the iTRV batteries with them.

The two 'good ones' are still working. They lasted around 40 weeks. They were re-charged and re-fitted for the winter.
One downside of these, if the device using them has battery level monitoring, it will no longer work. They either give 1.5v or give up. No in-between voltage, so no warning of charging requirement.
The odd one I now have, is used in a battery bluetooth mouse. Lasts for ages..... but I'm not monitoring it.

 

One downside of these, if the device using them has battery level monitoring, it will no longer work. They either give 1.5v or give up. No in-between voltage, so no warning of charging requirement.

Good point.
That could be problem in some applications.
It's not for my use in a door lock, since I always carry a backup key which will open it manually.

My four units are still working, but it's been less than a month.
Time will tell.