Wednesday, November 09, 2011

New Lithium Rechargable Battery Type in AA Format - LiFePO4

Thanks to Blog reader Hayami, I've got known to this "new" battery type and product.

This new rechargeable Lithium technology is different from the conventional Lithium-ion or polymer ones, the native voltage is at about 3.45V and with a nominal rated voltage at 3.2V after some use. This voltage is actually very close to the added up voltage of two fresh disposable AA alkaline or lithium batteries. It is called the Lithium Iron Phosphate, or LiFePO4 in chemical term:-

(Source: Chinese ZOL Forum)

As we can see from the above Wiki article, LiFePO4 does have many advantages over the other conventional Lithium rechargeable technologies. Yet, it shares the advantages of other lithium rechargeables such as no memory effect and a very low self-discharge rate.

Unlike the conventional Lithium rechargeables, no external voltage regulation is required to match the "1.5V" (x2) voltage requirement, which makes now it is possible to make AA sized battery in which including such a voltage regulation circuitry is almost impractical.

As for the internal resistance of the LiFePO4, it is less than 100 mOhm as specified, which is close to the rated 90 to 150 mOhm of the Energizer disposable AA Lithium L91. But however, since we use four ("1.5V") L91 in our Pentax AA DSLRs whilst only two are needed for the LiFePO4 (with two other dummy battery conductors to be inserted in series and used in conjunction), the total battery internal resistance is halved in comparison, as a result. This is considered still much relatively safer to use the NiZn rechargeable AA as its internal resistance is only at about 5 mOhm per battery unit only, which is considered just too low and too dangerous, as it might cause damage to device depending on the design of its circuitry.

And, here is an article which shows the inside of a charger product that is widely available at Taobao (aka the Chinese e-Bay). It seems that the charger is well made with good materials used and workmanship. The charger is manufactured by a Hong Kong vendor with factory in the mainland China btw.

The LiFePO4 charger is also available in USB format, by a different Chinese manufacturer, though:-


Nevertheless, one of the least drawbacks of the current LiFePO4 AA in the market is about its lower rated capacity in mAh, which is at 600 only. But with its superior voltage regulation throughout its whole discharge curve, it has been widely reported that the battery performance and life is still superior than all those NiMH rechargeables which are rated at 2,000mAH+ something, for most cases. Below is one set of the tested discharge characteristics for two different samples as posted:-


After all, my set of 4 LiFePO4 AA batteries (with 4 dummy AA conductors) will arrive very soon. I will test it more thoroughly this week and shall write an user report/review of mine later on. But as you can see in all the above Chinese web-links, most of the user comments are very favourable and positive, with various different kinds of devices used, including DSLRs, DCs, torches and RC toys. Besides using that in my K-x, I am eager to try that in my Tayami QuickDrive (QD) toy racing car and see how faster my car could get with the increased power but yet far less weight that put inside for the batteries! :-D


K-x Battery Issue Re-visited (with the Latest Firmware)

Better K-x Rechargable Solution? Is the NiZn Safe?

AA Battery Chargers Fully Compared (4 Models)

Overclocking Your Pentax (AA Battery) DSLR(s)!?

Six Years of AA Battery Pentax DSLRs

When 1100mAh Li-ion RCR-V3s Outperform 2500mAh+ NiMH AAs ..

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