Those high-current lithium AA and AAA cells

[Mark Hammer]

Ali Express keeps stuffing my mailbox with ads for various high-current rechargeable lithium batteries.  The idea of 6800mAH from an AAA, making an 8-pack a small powerful source of clean  power, is quite seductive.

In past (and I mean past), several of us here had recommended to people plagued by noisy supplies that a 6-pack or 8-pack of C or D cells could provide a valid alternative.  But AAAs are even more compact.  Not quite as cheap as a made-in-China (Caline, Amoon, Donner, et al) power brick, but it reduces AC outlet needs by one.

Any caveats to note?

[R.G.]

The biggest caveat is that 6.8 A-Hr in a AAA is likely to be a tad exaggerated. There is a history of ebay and aliexpress lithium batteries being over-advertised.

It is great if it's true, but verify.

A point to consider is that the electrochemical nature of lithium ion cells is a cell voltage of 3.6V nominal. Any lithium AAA would have about that voltage. Lithium-ion doesn't come in 1.5V cells. A better choice would be three 18650's (between C and D size) and a regulator of a couple of dropping diodes.

There are many newer sizes of LiIon cells, but the 18650 is a well-known standard, widely produced and economical (for Li-Ion).

[drdn0]

I reckon you'd have much better luck using 12/18v tool batteries - stacks of capacity, proven provenance and not that expensive.

Yes, you may need to regulate down to 9v but I'd trust that over an AliExpress battery pack any day off the week

[Rob Strand]

Something to factor into mAH numbers is the voltage.

The base voltage of a lithium ion battery is 3.6V (to 3.7V).   If you were to use a 100% efficient DC/DC converter to convert that to 1.5V the output current is (3.6/1.5) = 2.4 times higher.   The Ah rating also increases by the same factor.

If you look at name brand 18650 cells they are around 2Ah to 3.4AH.  So that translates to 4.8Ah to 8.2Ah at 1.5V.
[As RG said, these are almost *the* standard size for lithium ion batteries.]

https://www.batteryskills.com/18650-battery-capacity-chart/

So getting 6000mAH from a 1.5V AAA sized package seem very unreasonable.

If you look at some name brand AAA lithiums, they are only 1000Ah to 1250Ah.  Far more reasonable and in keeping with the 18650 ratings.
(Battery volume 3.9cm^3 vs volume 16.5cm^3, about 1/4 the size.  1/4 of 6000mA average for the 18650 is 1500mAh.   The converter will take up space in the AAA so the actual mAh will be less than 1500mAh.)

https://data.energizer.com/pdfs/l92.pdf

It's very rare to have large technology jumps in battery technology and it took some years to creep from 2Ah to 3.4Ah cells.

[I didn't mention these name brand AAA's are not rechargable.   Usually that means higher ratings for the size.]

Something to be aware of is these things have a DC/DC converter inside.  The DC/DC converter could be noisy.  It could misbehave under light loads.   The DC/DC converter will vary over brands, models, even time (due to revised or changed designs).

[printer2]

Bought some step down modules from China, forget the ones with the LM2596 chip, the XL4015 is better. From a post I did previously.


"Let us start with the bottom one in the picture. Should be ok charging batteries as long as you do not want current limiting. 250 mV ripple at 12.6V (all measured at 12.6V) and a speedy 16.7 kHz. But it does have mounting holes.

The three trimmer one in the middle runs at 72 kHz. Wonder if my high voltage module running at close to the same frequency will cause any problems? Another concern is its 0.5V ripple. One ray of sunshine, as you reduce the voltage out the ripple reduces somewhat the same amount.

The top one (XL4015) fairs a little better. It has 180 mV ripple, best so far. Now the biggie, running at 200 kHz. I think this is the one I will be using. Still want to into the ripple though. I guess I better order a few more of the high frequency one."

[antonis]

Should be ok charging batteries as long as you do not want current limiting.

There is (or should be) a clear distinction between "current limit" and "constant current"..    
(the former saves the supply where the later saves the battery)

[ElectricDruid]

A point to consider is that the electrochemical nature of lithium ion cells is a cell voltage of 3.6V nominal.

3 x 3.6V (10.8V) sounds like a good voltage for pedals. Even 4 x 3.6V (14.4V) would be fine. But as drdn0 said, power tool battery packs would be the way to go, either 14.4V or 18V (5 x 3.6V). And then you can use your existing collection of power tool chargers!

[Rob Strand]

Lithium Ion battery chargers aren't just current limiters.  They have a number of special features to help prevent damage to the battery and also reduce the risk of the battery exploding.   There's a lot of info on the web.  Also special chips are available, you can see the kinds on features they incorporate from the datasheets.   The series cells like in laptops typically have cell balancing circuits.

[printer2]

I took part in the running of a solar powered race car with Li batteries. Others were suppose to develop a battery management and telemetry system, I was skeptical about the system working by race time and against my boss's instruction I used a couple hundred from my repair budget and made a dumb system using comparators to disconnect the battery pack when a cell went outside its safe area. Each cell has the maximum and minimum voltage set-points as well as one for over current and over temperature.

There were some chips to manage those functions back then, think I went the way I did so that even a Mechanical student could troubleshoot it with just a multimeter on the road. Happily our car finished the race, we won 3-4 out of ten awards for our car (been a while, think four but at least three), unheard of on a virgin run. One car's battery was not so lucky and a quarter of the car got crispy before the fire was put out (fire extinguisher in each driver area).  Almost forgot, there is also a maximum charge rate but we did not have enough juice that it would be an issue.