In my eneloop review for Professional Photographer, I examined the performance of eneloop rechargeable batteries to see if they really do retain their charge over time, and if that convenience comes at a cost (i.e., reduced power).
The first day of testing, I decided the eneloop batteries could use a test run. Without charging the eneloop batteries, I used them in my Speedlights to photograph a variety of objects. I fired off a respectable 500 frames during my three hours of “testing.”
The next day, it was time to perform the real experiment, which included the test I discussed in my article on PPmag.com, as well as one additional test that actually took place first. Remember I used the eneloop batteries to power those 500 frames earlier? Well, I wanted to push this whole “no recharging” concept, so I let those eneloop batteries sit for a few days, without charging them. Then, I compared a standard set of rechargeable Ni-MH batteries (2650mAh) to the eneloop batteries (2000 mAh). The equipment I used for my experiment is as follows: three Nikon Speedlights, one Speedlight was set as the “commander” unit to fire the other two “remote” units, both set manually at full power. One remote Speedlight was powered by four eneloop batteries, and the other was powered by four 2650 mAh rechargeable batteries.
Taking the setup I described above, I fired a series of test shots (50 in all), recording the recycle time for both speedlights. On average, the standard batteries took 4.568 seconds to recycle the flash, while the eneloop batteries took 5.494 seconds. So, in this test, the eneloop batteries were an average of 0.926 seconds slower. Now, I know that’s slower, but don’t forget the eneloop batteries haven’t been fully charged. The results from this test might be comparable to actual use after long-term storage, as the batteries are packaged at less than full capacity when manufactured (~75% capacity), and I then further drained the batteries during my “free shooting” test. My conclusion from this test? The eneloop batteries definitely hold their charge better than my standard Ni-MH rechargables… and though it should be obvious why their performance is not quite as good as newly charged standard Ni-MH batteries. The graph below shows the recycle time, in seconds, on the y axis, and the shot number on the x axis. The red line depicts the eneloop results, and the blue line depicts the 2650 mAh results.
Now, the second test, which I focused on in the article, was performed after both sets (eneloop and the 2650 mAh) had been freshly charged. In this test, I pushed the boundaries of the flash — I decided to challenge the 150 shot “limit” I had read about on KenRockwell.com. At shot 155, I had to pause my experiment, as the Speedlights and batteries (both eneloop and 2650 mAH) had begun to overheat… they were quite warm/hot to the touch. I removed the batteries from the Speedlights and allowed everything to cool for two hours (see graph below – that’s the break in the line). After that, I resumed the test. In total, the batteries were able to power 213 flashes at full power… after that, they could not produce enough power to discharge the flash. Now, obviously I was able to push the 150 shot limit, but not practically. Additionally, if you look at the graph below, you will see that the recycle time length started to increase exponentially towards the end of the test. Again, eneloop is red, and 2650 mAh is blue.
This next graph depicts a segment of the entire test, shots 1-155:
Remember, at this point, both units were hot to touch and you could almost “smell” them. Both the eneloop and 2650 mAh batteries were removed from the Speedlights to cool down, and testing was resumed 2 hours later. This final graph depicts shots 156-213.
Another thing to note… These eneloop batteries reportedly take a few cycles of charging to reach their peak output, so future tests might even give the eneloop battery more of an edge:
“If stored with charge, it is possible that when you return to use the battery there may still be some charge left in the battery, therefore it will enable you to use it right then and there. Also, by keeping some charge in the battery, it will require you to “cycle” the battery fewer times until it reaches its peak charge. If you store them with no charge, you will have to “cycle” the battery multiple times until it reaches its peak charge.” (Source: Sanyo)
If you’re interested, you can return to my eneloop review for Professional Photographer, or you may explore an article further discussing the long-term discharge and capacity of eneloop batteries.
Betsy is a Michigan-based 
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I’ve got some problems with your review. The first test was done on partially charged batteries. How can you quanitfy if it had a little or a lot of charge left? I get the part about the eneloops needing a few recharge cycles for them to get their maximum charge, but the full drain versus partial drain is a bit confusing.
For the second test, it would be good to know which brand of nimh was used, were they brand new, a year old, how many charge cycles have they been subjected too, and which type of recharger was used? I’ve seen a fair amount of variance between 4 hour rechargers and quick chargers from different manufacturers between different nimh’s.
As best I can tell, the only real advantage the eneloops have is better off the shelf charge. I’d never consider relying on batteries that have sat idle for weeks or months, but instead would recharge them the day before I used them.
Eddie, the first test was done to simulate the eneloop’s claim that the batteries can be used off-the-shelf, no matter when they were last charged.
The “standard” Ni-MH batteries I used were Duracell brand. Brand new, and charged for the first time just prior to test #2. Actually, the first time I charged the eneloop batteries was just prior to test #2 as well.
Chargers used — I used the eneloop approved slow-charger for the eneloop batteries (as they’re not “approved” for charging in standard chargers). To charge the 2650 mAh batteries, I used an overnight charger (I am traveling right now, but I will find the specs when I am able).
One mistake but a little known one is that the Duracell brand of NiMH cells have excessive internal resistance which causes them to have a much shorter life span (charge) then almost any other major brand I’ve tested. The as common “Eveready” will last longer by a fair margin. Neither will work as well as the eeloops over time. Most of my 2600 mAh cells never charge to that level anyways.. they always fall short, sometimes by a lot and sometimes by a little. A another point of contention and little mentioned is that the high capacity cells do not always fit quite right into some electronic bays. They are a bit fatter and sometimes a bit shorter than a normal lower capacity cell. The eeloops fit everything without fail. The Evereadys are close but sometimes a tight fit. I have some knockoffs that work but are a bit too short at times.
My Duracells have all been tossed in favor of Eveready and eeloops. I do a slow charge with an 8 slot (two hour) soft charger and all have held up very well over the past year.