>> Yes, rechargeables have a lower total mAH capacity
>> that alkalines, etc, but their voltage/time curve tends to be much
>> flatter, especially for NiMH cells. If the thing you're trying to run
>> does well in the voltage range that NiMH cells tend to fall in as  
>> they
>> are discharging, then you can actually get *more* runtime from them
>> than alkaline cells.
>
> I could see that this could theoretically be true, but I doubt it is
> very commonly true of battery powered devices.

(early?) Digital cameras were famous for getting MUCH longer life from  
NiMH rechargables than from alkalines (not to mention infamous for  
really TERRIBLE performance on alkalines.  I don't think that this was  
so much due to the discharge curve flatness mentioned by the original  
poster, but because the alkaline batteries of the day suffered  
terribly under the high-discharge rates (with higher discharge pulses)  
that the cameras provided.  You can look at discharge curves for all  
sorts of batteries at http://www.candlepowerforums.com, both inside  
and outside of manufacturer recommended ranges.

Also note that while "rechargables have lower capacity than primaries"  
is an old rule of thumb, it mostly pre-dates modern NiMH technology.   
Duracell rates their AA alkaline as 2850 mAH, and their NiMH at 2650  
mAH, for example.  While the extra .3 V makes the engergy difference a  
bit greater, the difference in discharge curves throws in some  
uncertainty as well.   They're REALLY close.

I love li-ion batteries, though certainly not the price premium that  
equipment manufacturers charge for them.  Or their relative danger in  
unpackaged form.
The new low-self-discharge NiMH batteries are nice too; a close  
second, and near ideal for equipment taking standard AA sized  
batteries (not available or very expensive in larger sizes, though.)   
There's still packs of alkalines for the "disposable" items and the  
things that take "big" batteries, though.

BillW

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