Investigating the Westinghouse 3.2 V AA LiFePO4 cells

These are the latest generation of "green" cells being used for solar lighting applications and can be found, for example, in the solar lighting section of Wal-Mart.

I picked up a few of the 600 mAh AA/14500 variety to test and see what they can do.

An add replaced the OP's images. Bill

General Characteristics

They are identical in size to a regular AA cell, but lighter in weight. Each cell weighs 18 g, compared for example to 27 g for an Eneloop.

The nominal voltage is 3.2 V and this corresponds to the voltage seen under light load when freshly charged.

Charging

The cells are very unfussy about how they are charged. According to the LiFePO4 chemistry they should be charged with constant current up to 3.6 V and then constant voltage until the current tails off.

However, in practice these cells do not seem to mind being charged to higher voltages. If you charge them up to 4.0 V and remove them from the charger the extra voltage bleeds off until the voltage drops back down to 3.6 V or so.

This behavior seems to suggest the cells can be trickle charged with a low current such as would occur with the intended solar lighting applications, without needing complex charge control.

Discharging

Here, the cells seem to have the typical characteristics of the LiFePO4 chemistry. They have a relatively high internal resistance and do not do well with high discharge rates.

I measured the DC internal resistance at about 200 mΩ, a little less when freshly charged, a little more when discharged.

The following graph shows discharge tests through constant resistance loads. These correspond to approximate C rates of 0.5C, 1.0C and 2.25C. With true constant current discharge the voltage fall off at the end would be steeper.

The measured capacity compares well to the claimed 600 mAh.

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Conclusion

These cells are interesting, but not all that exciting. They are not A123 cells by any means. Possibly they would be a neat option for single AA LED lights where the head can take voltages up to 3.5 V.

Good report. I guess if ultra portability is important, these wll work. But, at 600mah, versus their 3-4x denser AA cousins, the voltage really has to offer significant improvements for us to consider

Thanks!

I might have to check them out next time im there...if i may ask what charger did you use to charge them.......

ptolemy said:

Good report. I guess if ultra portability is important, these wll work. But, at 600mah, versus their 3-4x denser AA cousins, the voltage really has to offer significant improvements for us to consider

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Since these, like all Li-ions, have negligible self-discharge, the most reasonable comparison to NiMH is LSD cells such as Eneloops.

Eneloop = 1.2V * 2Ah = 2.4Wh
Westinghouse = 3.2V * 0.6Ah = 1.9 Wh

So if the low voltage is fine, LSD NiMH are clearly 25% better. However, particularly in LED flashlights, two major benefits are realized with the higher voltage:

• boost converters are generally more efficient as the supply voltage approaches the LED's Vf of 3.2-3.5V, so if the converter should have an efficiency of, say, 90% at 3.2V, and 72% at 1.2V, they'd come out even.
• boost converters also frequently have difficulty giving high output from 1.2V, because the current required from the AA cell is about 3x the LED current. See, for example, the difference in turbo output on the Quark 123 vs. the Quark AA (same exact driver, with output specs given for different input voltages). So even if runtime is 20% less on low modes, the extra brightness on high may be worth it. The usual option here would be a LiCo (3.7V Li-ion) 14500, but as Mr. Happy mentioned, some lights (like the Fenix L1T) don't take well to over 3.5V.

I guess I'll have to look into getting some of these next time I'm at Walmart -- the ones I have ("Free Energy" brand) are only 400mAh, which is on the verge of uselessly low.

alfreddajero said:

if i may ask what charger did you use to charge them.......

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I don't have a proper charger, so I just cobbled something together with Eneloops, like this:

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Charge for about three hours or until the voltages equalize. As far as I can tell you don't have to be precious about the charging voltage on these things unlike lithium cobalt cells.

If I were going to use these cells a lot I would come up with a more permanent charging solution.

I wonder if these cells would do well in a Nitecore D10 just for use around the house and for backup.

alfreddajero said:

I wonder if these cells would do well in a Nitecore D10 just for use around the house and for backup.

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I use similar cells to these (battery station 14505 lifepo4) in a lot of my AA flashlights. With the Nitecore D10 they don't bring much to the table as brightness is about the same as Eneloop or any other battery chemistry. The regulation of the D10 keeps things in check and run time doesn't seem any better either.

Where I really like these batteries is in my fenix and quark flashlights. Both reward you with much higher output on lifepo4 then you would get with nimh or alkaline. And you don't end up losing modes in the fenix, which is a problem with 3.7v 14500's. Run time is mediocre at best though.

I have checked a couple of walmarts looking for the westinghouse batteries but so far no luck. I don't think these are an item that they regularly stock so prepare your expectations accordingly.

Okay thanks for the update, i guess in my case it will not be worth getting them.

supergravy said:

I have checked a couple of walmarts looking for the westinghouse batteries but so far no luck. I don't think these are an item that they regularly stock so prepare your expectations accordingly.

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If found, they would be in the garden section with the solar lighting.

cant believe no one has asked yet... how much do they cost?

jasonck08 said:

how much do they cost?

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$10/4

Not too bad... I believe 600mAH is very good for LiFePO4 cells.

On DX they have some 14500 350mAH LiFePO4 cells, these are much higher capacity and are about the same price per unit.

Have you attempted discharging them at 2C? What are the results?

jasonck08 said:

Have you attempted discharging them at 2C? What are the results?

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I have not done a 2C discharge yet but may do one later.

If im able to find the cells then it might just be worth getting a pack for the hell of it. As long as the light comes on then to me thats what really matters right.

jasonck08 said:

Have you attempted discharging them at 2C? What are the results?

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I have added a high load discharge test to the graph.

Mr Happy said:

I have added a high load discharge test to the graph.

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Thank you! Did the cell get warm at all during the test? Do you think it can go any higher... 3C or 4C? Thanks for the tests. It's very valuable information.

Regular LiCo cells usually have a max recommended max discharge of 2C, but I was under the impression that LiFePO4's can usually go a lot higher.

jasonck08 said:

Thank you! Did the cell get warm at all during the test? Do you think it can go any higher... 3C or 4C? Thanks for the tests. It's very valuable information.

Regular LiCo cells usually have a max recommended max discharge of 2C, but I was under the impression that LiFePO4's can usually go a lot higher.

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No the cell did not get more than very slightly warm.

Remember that these are regular old fashioned LiFePO4 cells, not the new breed of specially modified ones such as nano-phosphate or A123 Systems cells. Regular LiFePO4 chemistry has limited discharge rates due to the high internal resistance. You can see that by the way the voltage drops quite significantly at 2C in my graph.

Just got back from WM. Had to pick up a few things. I found these for sale, so I also picked up a pack to test ou.

They had 14500's and also 18500's. The funny thing about the 18500's is they were also rated at 600mAH, despite there 40% larger size.

I suspect that the 18500's may be under rated. I don't have anything that uses 18500's, otherwise I would have grabbed some for testing.

Mr Happy did you see any 18500's at your WM?

Once you get them charged up can you post what lights your going to use them in and how well they did, and what charger you used.

jasonck08 said:

Mr Happy did you see any 18500's at your WM?

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Yes, but I thought, "What's the point of making a bigger battery with the same capacity as a smaller battery?" So I didn't get any.