Lithium AA and AAA cells - interesting behaviour.

[paulca]

My mouse just told me that the battery in it is under 10% charge.

All normal, except it is currently powered by a lithium replacement AA cell. 

My understanding is that these would produce close to bang on 1.5V until the lithium dropped under cut out and would then produce 0V.

How does the mouse know it's 10%?

The only thing I can think of is... if they had the brilliant idea to use a "Fuel gauge" type affair and then alter the buck converter output to, say, 1.2V when close to lithium cut out.  Further they could just replicate the good part of the charge curve of a traditional AA cell.

I wasn't expect it in a set of 'amazon' AA replacements though.

[IanB]

I would say that when the lithium ion voltage drops below the minimum threshold of the step down converter, that it would not suddenly stop working (unless they designed an off switch into the system). Rather, what would happen is that the output voltage would gradually decrease as the input voltage decreases, especially when the mouse draws such a low current.

This is the sort of behavior I think you would see if you connected a DC/DC buck converter to a variable voltage supply, and then gradually decreased the input voltage while watching the output voltage? The converter would gradually begin to lose regulation and its output voltage would start to sag without suddenly dropping off a cliff.

[tom66]

It's possible it is clever enough to measure the lithium-ion battery voltage and adjust the 1.5V output as that gets low, I've not seen any that do that but it seems like an interesting idea to maintain battery SOC indication.

I don't think the converter is dropping out as the cell voltage would have to fall below the safe limit for a lithium cell, around 2.5V.

[IanB]

I think this could also be a deliberate feature of the cells, so that you have an early warning to change batteries, rather then experiencing a sudden failure at an inconvenient moment.

[Monkeh]

Are you sure you're not using lithium primary cells? They have a discharge curve like any other cell, if not necessarily as steep as alkalines. They certainly don't just drop to 0.

[Siwastaja]

Well, what can we say? We would need to know:
1) what was the actual voltage when you measure it?
2) did the mouse stop working soon enough after this warning, i.e. was it actually around 10% ballpark?

Lithium primary cells are indeed steeper than alkaline, but not a brick wall, nothing is.

And why would you think lithium batteries would have DC/DC converter inside!?    Li/FeS2 cells have natively voltage around 1.5V so are direct replacements for alkaline batteries. There is no need for the hassle of voltage conversion.

[paulca]

Are you sure you're not using lithium primary cells? They have a discharge curve like any other cell, if not necessarily as steep as alkalines. They certainly don't just drop to 0.

I get where you are coming from, but my understanding is that these are just small "lipo" pouch cells and a basic lithium management IC, similar to the 4056(?).

It the pouch is above ~3V, then buck to 1.5V.

If the pouch is below ~3V cut out.

If charge is connected, disconnect the output, charge the cell with a buck 5V->nV based on current draw.

This model does not provide a "low charge" indication.

If this is "real" and I need to test with a meter properly.  Then there is something else in their IC beyond the 4056 behaviour.  It may as others above hinted to not be a constant voltage output but a ratio to the cell.  Such... however.. a cell at 4.2V produces 1.7V and a cell at 3.0V produces 1.2V.  (figurative figures). They can be done to be "inherent" in the design of the buck converter

[IanB]

And why would you think lithium batteries would have DC/DC converter inside!?    Li/FeS2 cells have natively voltage around 1.5V so are direct replacements for alkaline batteries. There is no need for the hassle of voltage conversion.

I believe this topic is about rechargeable AA cells using lithium ion technology. They have a little USB socket on the side to recharge them and produce a regulated 1.5 V output. Like these, for example:

https://www.amazon.com/bump-1-5V-Rechargeable-Batteries-Keyboards/dp/B07NCDTMFV

They would be good for voltage sensitive devices that need a cell voltage over 1.3 V or so to work (poorly designed devices, but they do exist).

[thm_w]

If OP is talking about lithium-ion AA cells linked above, then yes some do drop the voltage output to 1.1V when the internal cell is almost dead.
Of course it would help if OP actually linked the product instead of us having to speculate.

https://web.archive.org/web/20230324191803/https://www.xtar.cc/news/XTAR-Improved-The-Rechargeable-1.5V-Lithium-ion-Batteries-221.html

[DavidAlfa]

Because you must measure the cell voltage underload.
So it migght be 1.5V in thge DMM, but drop to 1.3V when drawing 10mA.

The mouse probably measures the battery in max load conditions, whenthe LED is operated and the MCU is running.
Probably a short peak of 25-50mA before going back to sleep.

Just an example, last week I repaired another Tektronix with a depleted calibration NVRAM, with the DMM alone it measured 2.9V, so you might think it was OK, right?.
Well, when touching the probes with my fingers, the current was probably just few uA, but that was enough to drop the voltage down to 2.1V, and pressing harder went under 1.7V!

[Zero999]

There's no need for anything fancy. It's easy to build a buck converter which simply outputs 36.6% of the input voltage, which will give about 1.5V, with 4.1V in, down to around 1.1V, when the input has fallen to 3V, by which point the battery under voltage protection kicks in and it cuts out.

[thm_w]

There's no need for anything fancy. It's easy to build a buck converter which simply outputs 36.6% of the input voltage, which will give about 1.5V, with 4.1V in, down to around 1.1V, when the input has fallen to 3V, by which point the battery under voltage protection kicks in and it cuts out.

I'm not aware of any that work that way though, they regulate the output to 1.5V:
http://lichiwei.com/product.php?id=13

[tom66]

I would imagine that these devices are high volume enough now that you could build them to have a custom PMIC inside them.

Such a device could precisely measure the charge in and out of the cell and adjust the terminal OCV so that it matched a real alkaline, against something simple like an 8 point look up table.

But maybe I'm dreaming.

[Halcyon]

A word of warning with Lithium primary cells and wireless mice (could apply to other consumer products as well).

I have had issues in the past where a fresh set of Lithium cells measured a voltage higher than what you would expect from regular AA batteries. It was so high that the mouse refused to even power on until the cell voltage decreased slightly. To get around this, I partially discharged the batteries.

[IanB]

A word of warning with Lithium primary cells and wireless mice (could apply to other consumer products as well).

I have had issues in the past where a fresh set of Lithium cells measured a voltage higher than what you would expect from regular AA batteries. It was so high that the mouse refused to even power on until the cell voltage decreased slightly. To get around this, I partially discharged the batteries.

Not the kind of battery in this thread, but yes, I think Energizer Lithium cells start out around 1.8 V, which is too high for some devices. Same with nickel-zinc rechargeable cells, which also top out at a pretty high voltage.

[Siwastaja]

This thread was a train wreck from the beginning. There is only one meaning for "AA lithium battery", namely the primary cell. Recharging is absolutely forbidden.

If you mean a rechargeable lithium ION battery SYSTEM, which is not a "cell", nor "lithium", then say so.

[Gyro]

A word of warning with Lithium primary cells and wireless mice (could apply to other consumer products as well).

I have had issues in the past where a fresh set of Lithium cells measured a voltage higher than what you would expect from regular AA batteries. It was so high that the mouse refused to even power on until the cell voltage decreased slightly. To get around this, I partially discharged the batteries.

Not the kind of battery in this thread, but yes, I think Energizer Lithium cells start out around 1.8 V, which is too high for some devices. Same with nickel-zinc rechargeable cells, which also top out at a pretty high voltage.

On the other hand, you have Blink cameras, which won't even power up on a pair of fresh alkaline batteries, and must have Energizer Lithium cells fitted.

[tom66]

A word of warning with Lithium primary cells and wireless mice (could apply to other consumer products as well).

I have had issues in the past where a fresh set of Lithium cells measured a voltage higher than what you would expect from regular AA batteries. It was so high that the mouse refused to even power on until the cell voltage decreased slightly. To get around this, I partially discharged the batteries.

Not the kind of battery in this thread, but yes, I think Energizer Lithium cells start out around 1.8 V, which is too high for some devices. Same with nickel-zinc rechargeable cells, which also top out at a pretty high voltage.

They rapidly drop to about 1.6V under load - within 5 minutes in my experience.  (I built a voltage-based SoC monitor for a product that used these.)  So as long as the product can withstand the slightly higher operating voltage initially (higher leakage current for instance), they're usually fine.

[Siwastaja]

A word of warning with Lithium primary cells and wireless mice (could apply to other consumer products as well).

I have had issues in the past where a fresh set of Lithium cells measured a voltage higher than what you would expect from regular AA batteries. It was so high that the mouse refused to even power on until the cell voltage decreased slightly. To get around this, I partially discharged the batteries.

Not the kind of battery in this thread, but yes, I think Energizer Lithium cells start out around 1.8 V, which is too high for some devices. Same with nickel-zinc rechargeable cells, which also top out at a pretty high voltage.

They rapidly drop to about 1.6V under load - within 5 minutes in my experience.  (I built a voltage-based SoC monitor for a product that used these.)  So as long as the product can withstand the slightly higher operating voltage initially (higher leakage current for instance), they're usually fine.

Yeah. Standard alkaline cells are also around 1.65V initially and literally every device must deal with that in all operating conditions (temperatures, unit-to-unit variation etc.) so extra 0.15V is not that much, I'd expect these work in 99% of devices just fine (and that's the intended purpose, too).

[PlainName]

Dare one ask what the advantage of these are over traditional eneloops or other low self-discharge NiMH? And why do they all list capacity in mWh whereas normal types are in mAh? Seems to me to be scope for exaggeration: are they using the output voltage or cell voltage in working out the mWh?

A disadvantage, ISTM, is the convenience of a USB port for charging. If you're using them on, say, a cat flap that takes 4xAA then you need 4 off charger ports and cables, whereas NiMH is just one charger that will do 'em all in parallel.

[Veteran68]

I use a lot of Eneloops but as discussed their power curve is different and some devices don't like their lower nominal voltage, either not working outright or exhibiting very short battery life. I've started transitioning to more lithium rechargeable batteries and really like them. I also find them to last longer both in terms of battery life and total lifetime.

Not all rechargeable lithium batteries have a built-in USB charging port. I have AA and AAA lithium batteries that are charged in the same multi-bay charger that also charges my NiMH cells.

[PlainName]

Thanks. I missed the initial voltage being sensible and not triggering low battery warnings from the off

Do you have a favourite brand for the non-USB charging ones?

[Veteran68]

Do you have a favourite brand for the non-USB charging ones?

I like the EBL brand you can find on Amazon. I have these in 9V and also these in AA and have been quite happy with both.

[thm_w]

I highly doubt these rechargeable lithium AA or AAA's last longer than eneloop pro's (2450mAh for $2.50 from ikea). But I don't see them on: https://lygte-info.dk/ Anyone have any actual capacity tests?

The 9V cells 100% make sense and have more capacity than nimh for same or lower cost.

[PlainName]

Do you have a favourite brand for the non-USB charging ones?

I like the EBL brand you can find on Amazon. I have these in 9V and also these in AA and have been quite happy with both.

Super, thanks. The Mxbatt ones aren't available over here but there is another brand that looks suspiciously similar. However, with all of them we are looking at around £5 apiece, which is a bit steep. I'll have to think up a compelling use case...