Rayovac 4.0 Rechargeable AA 4-Count (Pack of 2) Review

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(More customer reviews)The product description of Rayovac 4.0 AA cells appears to be intentionally deceptive. It says "Rechargeable Battery with Lithium Technology", but did not mention anything about the battery chemistry, voltage, and capacity. On the front of the package it says "Compare to ADVANCED LITHIUM", and "Ready to use like LITHIUM". All these seem to give the impression that "Rayovac 4.0" is similar to the Energizer L91BP Lithium AA Battery, which has a higher operating voltage (1.6V) and larger capacity (3000mAh) compared to normal NiMH AA cells.
Upon closer examination, however, you'll see the fine print of "NiMH 1.2V" on each cell. Suspiciously, its capacity (mAh) is still not specified. So despite of all the hype, this is still a Nickel-Metal Hydride battery, perhaps with a trace amount of Lithium added to justify the claim of "Lithium Technology".
I tested four Rayovac 4.0 AA cells using my La Crosse BC-900. Right out of the package, they hold an average charge of 1485mAh, or about 70% of full capacity. After two more charge/discharge cycles, their avarege capacity improved to 2080mAh. This performance is nearly identical to that of Rayovac Hybrid AA Batteries, which I have tested many times before. Further examination also revealed that the (+) and (-) terminals of "Rayovac 4.0" are exactly the same shape as "Rayovac Hybrid". Therefore I'm convinced that those two series are in fact the same cell under different wrappers.
I really dislike the shiny wrapper of "Rayovac 4.0" cell. It makes the cell look too much like the Energizer Lithium AA cell, and it doesn't even mention "Rechargeable" on the wrapper. I can only imagine how many of those rechargeable cells were thrown out after first use, because people confused them with desposable cells.
On the other hand, the price for 8 of those "Rayovac 4.0" AA cells is less than half that of Sanyo Eneloop 8 Pack AA (as of this writing). This makes them an amazing value. It is much better to buy those, instead of trying your luck with other so-called "Ready-to-Use" rechargeable batteries from less reputable brands.
[Update on Feb 25, 2010]
Data on long-term self-discharge rate: I have tested four each of Rayovac 4.0 AA and AAA cells, after 100 days of storage at approximately 19 degree C. The average charge retained in both sets were exactly 86% of original. This is consistent with the self-discharge characteristics of Sanyo eneloop and Rayovac Hybrid.

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