Originally posted by Kguru I'm also curious, the alkalines are rated as 1.5V whereas the NiMHs are usually 1.2V, does that mean the camera can handle a range of 4.8V to 6V?
Nominal voltage varies based on many factors. As a battery is unable to provide sufficient current, voltage will drop. Alkaline AA batteries
rarely have a nominal voltage of 1.5V, especially not at the loads the K100D throws at it. They will also
fail to provide anywhere near the "charge" (in mAh) as most are rated with a measly 100mA load.
NiMH AA batteries typically charge at an electric potential of 1.5V, discharge at least an electric potential of 1.2V. Depending on the quality of the NiMH batteries, they may or may not be capable at providing even 1.2V at the current being drawn. Here's the data on the Energizer 2500mAh:
http://data.energizer.com/PDFs/nh15-2500.pdf
As you will see, pulling 2.5A (2500mA) from the Energizers will see voltage drop below 1.2V after about 0.7-0.75 minutes. I.e., as the batteries drop under 1000mAh "charge left," you'll see the LCD drop to "half" battery as current drops below nominal.
This almost matches my experience with the Energizers in the K100D, although I'm able to charge my nh15-2500 models to between 2600-2700mAh (as measured with a LaCrosse 900 series). Also note the performance for 1.25A (1250mA) is fairly similar and consistent, 1.2V or higher nominal for even beyond 1.5h, basically somewhere below 1000mAh "charge left" (possibly as low as 500mAh). The performance for 5A (5000mA) is rather dismal though, and consider the battery unable to support it at all.
Unfortunately, the data on the Energizer Lithium and Alkalines are not very helpful as they don't look beyond 0.5-1A (500-1000mA).
http://data.energizer.com/PDFs/l91.pdf http://data.energizer.com/PDFs/E91.pdf
As you can see, although the Lithium has a nominal voltage of 1.5V, and clearly provides over 3000mAh, but that's based on only a 0.05A (50mA) current draw -- the specs are clearly aimed at Alkaline AA batteries. Now looking at the graph next to it on page 2 for just 1A (1000mA), we see it provides well under 1.4V from second 1, and drops to under 1.2V in about 2.25hr, giving you about 2250mAh useful overall. The E91 Akaline in the same graph barely gives you a half hour at 1A, just over 500mA, and everything I've read says a 2A draw just kills Alkalines for sub 400mAh -- 1/3rd their nominal, rated "charge" in current-time (which is typically done at only 0.1mA). BTW, from what I've seen in other other tests, Lithiums can still provide over 2000mAh of 1.2V+ for up to a 2.5-2.8A draw though.
So considering I get about 1500mAh+ "usable" at close to the 2A draw of the K100D out of my Energizer NiMH 2500mAh AA batteries, for about 400-500 shots without any flash (half that for regular use of flash), and I've done more than 400 shots now with Energizer Lithium AA batteries and they are still "full" and most likely going to give me 2000mAh+ and around 500-600 shots without any flash (half that for regular use of flash), and these numbers aren't fabricated.
As always, NiMH require "care and feeding." I.e., they are leaky, so they need to be charged regularly (I never got a full month), although Sanyo Eneloops are supposed to be far less leaky. They can also have a "memory effect" -- and the Sanyo Eneloops are
no exception to that, with many people complaining they need a full 3-4 uses and recharges to reach their original charge capability. Using a charger with a full discharge-charge really helps, especially if you
always and fully discharge your NiMHs when you take them out. I do this with my Energizer NiMH 2500mAh to great effect using a LaCrosse 900 series that are sub-$40 at Amazon.
The LaCrosse 900 series are not the best chargers compared to ones that cost $100+, and there are documented issues with using the 100/200mA discharge/charge where the Delta-V is so low the charger doesn't detect the batteries are full. But I don't use the full cycle/refresh of the charger (that's really only necessary for older NiCD), and just use the 250/500mA and 350/700mA discharge/charge cycles (there is also a 500/1000mA cycle, but I don't use it, it's worth the extra few hours to get a full discharge/charge -- I've had a miscycle when I've discharged that fast). Doing that keeps my Energizer NiMH 2500mAh batteries fresh, always up to a full 2600-2700mAh, and a solid, capable 2A+ output that the K100D requires.
As others will recommend, the Sanyo Eneloops seem to hold charges longer. But I still recommend the full discharge/charge cycle. Some quick chargers do this now, although most don't.