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.
These have an internal Li-ion battery (likely about 3.6V) which is then dropped to a regulated 1.5V output by an internal buck switching regulator.
Their Ah rating is just comparable or slightly better than NiMH, but their Wh rating is significantly greater due to their higher ( and constant) output voltage, which may or may not be significant, depending upon the device being powered.
They are also rated for more lifetime charge-discharge cycles.
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 each battery doesn't have a USB-C charge-port as many of the others do, as it uses the included charging station instead.
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 that stops working at about a 1.2V/battery voltage, 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 they are completely discharged).
Hopefully these Li-ion's, which maintain a constant 1.5V output until discharged, will last longer in that application.

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 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.

Now, nothing 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: