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Customer Review

179 of 182 people found the following review helpful
5.0 out of 5 stars Best value if you're looking for Higher-Capacity Pre-Charged AA cells, June 3, 2011
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This review is from: Powerex MHRAAI4 Imedion AA 2400mAh 4-Pack Rechargeable Batteries (Electronics)
Ordinary 'high-capacity' NiMH cells typically advertise charge capacity of 2500-2700mAh (for AA), but they all suffer from rapid self discharge problems. That is why I switched over to low-self-discharge (also called 'Pre-Charged') rechargeable batteries more than four years ago, starting from the original SANYO eneloop. Over the years I have tested many other name-brand LSD cells such as Rayovac Hybrid and Kodak Pre-Charged, all with great results.

The only drawback of LSD cells is lower capacity. First-generation LSD cells are typically rated at 2000-2100mAh. Recently, I have seen arrival of second-generation LSD cells with higher capacity, such as these IMEDION AA 2400 mAh low self-discharge batteries. Here are my test results, using the La Crosse BC-900 battery Charger/Analyzer:

- Right out the package, the average remaining charge is 1880mAh for a set of four Imedion AA cells. This is about 78% of the rated capacity, which suggests those are indeed low-self-discharge type (ordinary NiMH cells typically arrive exhausted)

- After just one Charge/Discharge cycle, the average capacity improved to 2455mAh, or 2% higher than rated capacity. This number remains the same in subsequence cycles. Again, this performance suggests that those cells are LSD type (ordinary NiMH cells typically takes ~5 cycles to slowly approach their rated capacities)

Just for comparison, here are my test results for other brands of LSD cells:
- Sanyo Eneloop XX: Rated 2500mAh, measured ~2600mAh (4% higher)
- Yuasa Enitime PLUS: Rated 2500mAh, measured ~2400mAh (4% LOWER)
- Lenmar R2G AA: Rated 2150mAh, tested ~2030mAh (6% LOWER)
- GP Recyko NiMH AA: Rated 2100mAh, tested ~2230mAh (6% higher)
- UltraLast Green Everyday Precharged: Rated 2100mAh, measured ~2200mAh (5% higher)
- SANYO eneloop (2nd-gen): Rated 2000mAh, measured ~2130mAh (6% higher)

The measured capacity of IMEDION AA cells (2455mAh) is higher than all others except for Sanyo XX (2600mAh). However, as of this writing, the Sanyo XX costs nearly twice as much as the Imedion. That makes those Imedion LSD cells a much better deal compared to Sanyo XX. When comparing Imedion to Sanyo eneloop, you pay ~15% more for ~15% increase in capacity. So again, this makes the Imedion a great deal.

One important side note: The Imedion AA cell is quite a bit thicker than normal alkaline cells. So they may not fit in appliances with tight battery compartments. This is actually a common problem with high-capacity NiMH cells. I don't have a pair of calipers to measure the cell diameters. But in term of relative 'fatness' of various AA cells, I can arrange them in the following order:

IMEDION > Sanyo XX > Sanyo eneloop > Rayovac Hybrid > Alkaline

[Update on Oct 23, 2011]
Tested a pair of Imedion AA after 5 months in storage. The average remaining charge is 2125mAh, or 86% of the original capacity (2470mAh). This charge retention rate is almost as good as that of Sanyo eneloop.

[Update on Mar 31, 2013]
Tested a second pair of Imedion AA after 17 months in storage. They retained 75% of original charge. This means the Imedion's self-discharge rate is just slightly faster than that of eneloop. For all practical purposes both are excellent.
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Tracked by 11 customers

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Showing 1-10 of 42 posts in this discussion
Initial post: Jun 4, 2011 6:28:52 PM PDT
R. Anand says:
I enjoyed your review but I am concerned about the non-standard size. I assume the larger size accounts for the larger capacity?

On the product page, there is a scathing review from N. Jones regarding his miserable experience with 24 of the batteries. What do you make of this?

As always I appreciate your insights!

Thanks

In reply to an earlier post on Jun 4, 2011 7:50:21 PM PDT
R. Anand,
Strictly speaking, the IMEDION is not a 'non-standard size'. Ordinary alkaline AA cells have a diameter of 14mm, but the allowable range is 13.5 - 14.5mm. Most high-capacity NiMH cells are near the high end of allowable diameter, presumably because they need to put more 'stuff' into the metal can.

I have no idea why another reviewer had such bad exoperience with those Imedion pre-charged cells. If you look at the product page for original eneloop, there are about 5% of 1- and 2-star reviews too.

Posted on Jun 28, 2011 9:17:27 AM PDT
Bowser B says:
Thanks NLee, for doing this comparison test. I often wonder about real vs advertised capacity. I've used Powerex 2700's for several years along with one of their earlier 8-cell chargers. Since Powerex is not a major "name" brand selling for lower than name brand prices, I couldn't help but wonder if its claimed capacity was real.

In reply to an earlier post on Jun 29, 2011 7:36:42 AM PDT
Bowser,
PowerEx is a well-respected brand name among photo and flashlight communities. The company actually manufactures its own batteries in Taiwan/China. In contrast, none of the major US battery companies (Energizer, Duracell, Rayovac) actually make their rechargeable batteries. They simply put their brand name on batteries made by other manufacturers.

On the other hand, there are many other lesser-known brands of rechargeable battery available from Amazon (Zeikos, Delkin, Bower, Lenmar, Tenergy, DigiPower, etc.). For those brands you are correct to approach with skepticism.

In reply to an earlier post on Jul 13, 2011 2:59:29 AM PDT
[Deleted by the author on Jul 13, 2011 2:59:46 AM PDT]

In reply to an earlier post on Jul 13, 2011 3:00:01 AM PDT
DWD says:
Lee, the recharge count on the SanyoAA is 500 I think. What about these? Since I use several Canon 580EX IIs when I'm on location doing photography, the extra power over the original 2100mA Enloops would be nice to have, which would be roughly (using 4 batteries) 1200mA more power.

In reply to an earlier post on Jul 13, 2011 9:26:02 AM PDT
Last edited by the author on Jul 13, 2011 9:30:42 AM PDT
DW,
The Imedion cells all claim "500 cycles" in lifespan, same as that for Sanyo XX.

By the way, switching from four 2100mAh batteries to four 2400mAh does not give you more CURRENT (definitely not 1200mA). But it does give you ~15% more ENERGY.

Energy = Power * Time = Voltage * Current * Time

Your photoflash unit will consume the same power no matter what NiMH cells you put in it (as long as the battery voltage remians the same). So 15% extra Energy translates to 15% longer run time, or 15% more flashes in this case. For example, if previously you are able to get 500 flashes from a set of 2100mAh cells, then you can expect 575 flashes from a set of 2400mAh cells.

In reply to an earlier post on Jul 13, 2011 11:03:51 PM PDT
DWD says:
Yes, thank you. that's what I meant. Of course you get no more volts because there are the same number of batteries all with the same voltage.

Posted on Oct 25, 2011 10:53:56 PM PDT
C. Cannon says:
NLee: Thanks for your posts. I have 32 Imedion AA batteries and have been happy with them thusfar. Will storing the charged batteries in the freezer or refrigerator slow down the discharge rate? If so, is the freezer better than the refrigerator? Also: Do you recommend putting new batteries through a conditioning cycle? Thanks

In reply to an earlier post on Oct 26, 2011 12:27:55 PM PDT
Last edited by the author on Oct 26, 2011 12:29:57 PM PDT
C. Cannon,
As a rule of thumb, every 10 degree C higher temperature makes the battery's self-discharge rate double. That means if you store your cells at 0 deg C, you can slow down their self-discharge rate by a factor of 4 compared to storing at 20 deg C. This practice is useful for ordinary NiMH cells, which may lose 30% charge in a month at room temperature. But for low-self-discharge NiMH cells, it is hardly worth the trouble.

I typically run my new rechargeable cells through the Discharge/Refresh operation on my BC-900. This will exercise the cells for 3-4 complete cycles, to make sure that they reach peak capacity. Again, this practice is more important to ordinary NiMH cells. For LSD cells they typically can reach 95% capacity after just one complete Discharge/Charge cycle.
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