Mr Happy
Flashlight Enthusiast
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.
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.
Ad removed
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.
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