Duracell Mobile Charger With 2AA And 2AAA Pre Charged Rechargeable Nimh Batteries, CEF23DX4N Review

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(More customer reviews)The Duracell Mobile Charger (CEF23) is an extremely versatile charger. It actually has two operating modes, as selected by the MODE button:
1. As an AA/AAA NiMH battery charger, or
2. As an USB charger for USB-powered devices.
In battery-charger mode, the unit is a smart charger that accepts 1-4 AA/AAA cells in any combinations. The charger can be powered by either 100-240V universal AC input, or 12V DC input. This means you can also operate it from your vehicle's cigarette lighter adapter. Note that the car adapter is included in the CEF23DX4N, but not in the CEF23DX2.
The charging current is 550mA for each AA/AAA cell. So it takes about 4 hours to full charge up the included 2000mAh low-self-discharge cells (which are the Duracell-equivalent of Sanyo eneloop). I consider this a good compromise between shorter charging time and longer battery lifespan. Once charging is done, the current is reduced to 25mA (actually 0-50mA pulsed at 50% duty cycle) in trickle charge mode.
One really nice feature of this charger is that it has four individual battery status indicator lights. The status light for each cell turns RED when charging, GREEN when the cell is fully charged. It will even blink if you accidentally inserted an alkaline cell.
In USB charger mode, the unit generates a regulated 5-volt supply at its USB socket. You can then connect an USB-powered device (such as IPOD charger) to this unit. Input power for this USB charger can be from one of the following sources:
1. From 100-240V universal AC input,
2. From 12V DC input (car adapter), or
3. From four AA/AAA NiMH cells in the battery compartment.
The third way is the most interesting, because in case of emergency, you can even use 4 alkaline cells to power this USB charger, in order to charge up your cell phone's battery.
I must say that this charger is really well designed. It is a great bargain even if all you need is a simple battery charger. The USB charger mode is just an extra bonus.
[Update on Oct 7, 2010]:
Duracell has discontinued the excellent CEF23 charger (at least in the US) last year. So prices for the remaining inventory have skyrocketed. The replacement product (Duracell Go Mobile Charger) only charges in pairs, and does not contain an USB charger.
- If you just need an inexpensive 2-cell charger that can handle individual cell, consider the Sanyo eneloop MDR02.
- If you need a good 4-cell charger that can operate from 12V cigarette lighter adapter, consider the Targus LCD2700 with LCD Display
- If you need an advanced charger that can operate from 12V CLA, consider the La Crosse Technology BC500
- If you need a good 4-cell charger that can operate from 12V CLA _and_ can power an USB port using internal batteries... Sorry! Your best hope is to look for an international version of CEF23.
[Update on Dec 1, 2010]
Just in case anyone is still interested in this charger: I recently found out that its USB port is capable of supplying 1000mA output current - even though the spec says 500mA only. I discovered this by accident when using it as a portable recharger for my Archos 5 500 GB Internet Tablet.

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Amazing Rayovac 4.0 Rechargeable AA Batteries 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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