AA Li-on - how can they be AA

[michael newport]

Lithium-ion = 4.2 V/cell? I see quite a few adverts for Li-on AA batteries (~1.4V) How can this be?

I bought some "quality" Li-on batteries and they measure 1.75V. Cheapo ones measure 1.45V

from the net - seems it's 1.2V/cell really:- (is all a bit confusing)

Lithium-ion

The nominal voltage of lithium-ion is 3.60V/cell and represents three nickel-based batteries connected in series (3 x 1.20V = 3.60V). Some cell manufacturers mark their Li-ion as 3.70V/cell or higher. This offers a marketing advantage because the higher voltage boosts the watt-hours on paper (voltage times current equals watts). The

3.70V/cell rating also creates unfamiliar references of 11.1V and 14.8V when connecting three and four cells in series rather than the more familiar 10.80V and 14.40V respectively. Equipment manufacturers adhere to the nominal cell voltage of 3.60V for most Li-ion systems.

How did this higher voltage creep in? The cell manufacturer plots the voltage of a fully charged cell that measures 4.20V, discharges it at

0.5C to 3.00V and takes the mid-way point. For Li-cobalt the mid-way point is about 3.60V. The same scan done on Li-manganese with a lower internal resistance gives an average voltage of about 3.70V. It should be noted that the higher voltage is arbitrary and does not affect the operation of the portable devices or the setting of the charger.

The phosphate-based lithium-ion has a nominal cell voltage of 3.20 and

3.30V. This makes this battery incompatible with regular Li-ion and their chargers.

[dennis]

AA is a size not a chemistry. You can buy carbon, zinc, alkaline, various lithiums (and others) in both primary and secondary cells in AA size.

Don't buy one that your equipment can't take or there may be damage.

[The Natural Philosopher]

Then they weren't li-ion batteries

[michael newport]

Yes - but I was wondering how 1.4V (AA "size") can be derived from a 4.2V cell.

[Tim Watts]

They are not Li-Ion - they are metallic lithium - and they're primary cells, not secondary (rechargeable).

[Graham.]

Look again at those AA cells you bought. They may be Lithium, but I can't see how they can be Lithium Ion with the terminal voltage stated.

[michael newport]

These are the ones - with charger. (?)

[michael newport]

link as sent in reply to Tim

[Tim Watts]

Well, it cannot be LiFePO4 (the common form of Li-Ion) - that's 3.2V. It's not Lithium Polymer either.

Looking at this:

the pictures clearly say "Ni-MH".

I would say the seller is talking crap.

[The Natural Philosopher]

they say 1.5v, 3.7v and 4,2v on them in different places.

I THINK they are 1.5v when 'fully discharged' - but that level of discharge on a Lipoly will f*ck them forever.

Oh..no - its those cunning chinese again....

"KENTLI common polymer lithium ion battery technology through a voltage converter, the output voltage of 3.7V 1.5V lithium converted into a voltage output, and is fully compatible alternative to traditional batteries, completed a major initiative in the field of traditional standard cell, making lithium batteries to the development of generic batteries solid step forward."

so they have some sort of voltage regulator inside to drop the volts down to 1.5V

They claim its patented, but I can find no record of that patent anywhere.

ZL200820043879.8 is the alleged patent number

I bet its just a transistor resistor and zener diode and they get hot when discharging.

And blow up when shorted.

[The Natural Philosopher]

Its the kentli things. As I said they have a regulator inside so they LOOK like 1.5v AAs but they are in fact 3.7/4.2v cells regulated down.

Dodgy as hell.

[Capitol]

Or is there a regulator built in?

[The Natural Philosopher]

It is the latter, though how good it is, is a moot point.

Done properly with voltage and current sensing and a diode for charging it could be rather cute.

[Paul]

Looking at the discharge curve and other info I suspect they have DC-DC converters to give 1.5V out from 3.7V cell.

Paul.

[Capitol]

I had fun with a wireless rechargeable house phone last week. It uses 2 x 1.2V aa Nimh cells. Having deduced that the batteries probably had died, I went into my stock and found a couple of fully charged ones(1.4/.5V) popped them in and the phone still didn't work. Discharge rate was checked and operating voltage measured. All apparently OK. Replaced them with ZnC cells and the phone worked. Bought some new rechargeables from Amazon and the phone works. I can only assume that the internal dynamic resistance is critical in this application.

[Tim Watts]

I see. Somehow it seems like a bad idea...

[JHY]

Excellent idea in fact because it give you the much better performance of an Li-On and fixes the problem with the voltage dropping at all until the battery is flat.

[Graham.]

Look what I've found. All is at last reviled.

[The Natural Philosopher]

better than I thought. Proper smps

[Graham.]

Let's say 90% efficient. With four cells, wouldn't that be 60% overall?