While I definately leave the equipment and experience questions to Bill S, Ice Dawg, and s, when it comes to gadgets and handheld technologies, this is right up my alley.
Using rechargables (ie. NiMH, Li-Ion, etc), will definately get much better power duration than you would with alkalines. The rechargeables aren't as good for short burst power requirements but offer a more consistent and longer lasting power source. Thus when using for handheld items like GPS's, and digital cameras I wouldn't bring anything else. Personally, I use Nexcell AA 1800 Mah NiMH cells for both my GPS (Garmin eTrex Vista) and digital camera (Nikon Coolpix) when moutaineering. The NiMH and Li-Ion batteries are also less weight as well which is also a bonus.
There are two things to be concerned with on rechargeables though. The NiMH and Li-Ion rechargeables will slowly lose their charge over time. So, if you have them sitting around for any extended period (+1 week) you'll be starting with less of a charge. Second consideration is temperature, which is a big one when moutaineering. NiMH and Li-Ion do lower their power output when cold. This effect can be quite noticable at even 50 degrees let alone 0 degrees. The life of the battery will also decrease dramatically. For things like the GPS, this isn't as much of a concern as it doesn't draw a lot of power but the camera will. So, what I do is keep the batteries somewhat close to my body. If that isn't an option, put the cold cells in your glove and warm them up prior to use (then keep the device close to your body). This will help in solving this problem.
If you need a power source that is reliable in the cold, Lithium is the way to go.
Hope that helps!
This might be a good question for Bill S and others who love their GPS, Digital Camera's, etc.
Recently after using regular disposable alkaline batteries in my Digital camera for a long time I changed to using rechargeable NMH batteries and noticed a huge difference in performance (they lasted 4 times as long)
Does anyone have any experience how these batteries perform in very cold conditions or used with other devices like headlamps, GPS, etc. How do they compare to lithium batteries or any of the other kinds out there
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There are several kinds of rechargeable batteries that will fit in and work with your digital camera (can't say anything about specifics without knowing what basic battery it takes, but I am guessing if you used disposable alkalines, it is AA). To say a bit about the different chemistries - A good website with lots of technical info is the Energizer website http://www.energizer.com/ (or maybe I should say "was", since the "Technical Info" link seems to be broken right now). The common rechargeables available in AA are NiCd (lower voltage than standard, shorter life per charge, "memory" problem, but still, lots cheaper in the long run than disposables, cold problems similar to standard alkalines), NiMH (nickel metal hydride - standard voltage, good lifetime as you found, little or no memory problem though you should know there are several different configurations for different applications, cheap in the long run, slightly better in cold than alkalines), and rechargeable alkalines (definitely NOT the same as standard alkalines - NEVER try to recharge a standard alkaline or any battery not specifically marked as rechargeable - very similar behavior to standard alkalines, very cheap in the long run, but do have a little memory problem). Lithium ion batteries are not available in AA size, largely because they are approximately double the voltage of standard carbon-zinc or alkaline cells. They are rechargeable, though, and have essentially no memory problem, plus are pretty good at low temperatures. Lithium-iron cells, on the other hand, do come in AA size (called "photo batteries" in your friendly WalMart or camera store), are about 60 percent the weight of a standard alkaline (not "half", as some people claim), and behave very well at low temperatures. I have used Li-Fe down to -30F in flashlights and tried to use them in GPSRs and other electronic devices having LCD displays - the LCD displays don't work at those temperatures, although the rest of the widget did work, as evidenced by its feeding data to a (warm) computer. Several problems with Li-Fe - they hold their voltage until shortly before they die, which is why the avalanche beacon people say "never ever use Li-Fe in your avy beacon." The "battery life" meter in your widget will indicate lots of life left until the last few minutes before the batteries die. Li-Fe are very very expensive. However, in a flashlight at 3-season temperatures, the cost is slightly less per hour than standard alkalines, and at subfreezing temperatures, is much less than alkalines (if you can get the alkaline to work at all). I have used Li AAs in GPSRs on Denali (sub zero most of the time) and winter backcountry ski tours (Tetons, for example, subzero most of the time). The Li AAs are lighter than the NiMH and in many applications are longer lived. By the way, the amp-hour rating of a battery is dependent on the drain rate. Some batteries are designed for a high drain rate and others for a very slow drain rate. Flash units and digital cameras are high drain rate applications, so read the specs on the NiMH cells you are buying to see what applications they are designed for. Li-Fe are designed for fairly high drain rates, according to the Energizer literature I have.
My experience with NiMH and Li-Fe in very cold weather is that the lithiums outperform (lifetime) the NiMH (even supposedly high capacity ones). So if you expect to go through a set of batteries during a cold trip, I would go with lithiums - longer life on a set, and the replacement sets are lighter. But if you can go through the trip on a single charge (or are carrying a solar charger anyway and will have sufficient guaranteed sunlight), go with the NiMH (my little solar charger doesn't give enough charge on a typical winter day, and I am not willing to carry my larger charger on a ski tour). For around the local neighborhood and day trips, I use both alkaline rechargeables and NiMH AA rechargeables.
Congrats on Denali and thanks for being such a great contributor to this site.