On Nov 1, 2009, at 6:35 AM, Sean Breheny wrote:

> On Sun, Nov 1, 2009 at 2:51 AM, Peter Loron  
> <peterl@standingwave.org> wrote:
>> You also need to take into account the discharge curve of the battery
>> type in question, as well as the consumption of the device you're
>> trying to power. 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.
>>
>
> Hi Pete,
>
> I could see that this could theoretically be true, but I doubt it is
> very commonly true of battery powered devices. The end-point voltage
> of NiMH is about 0.9V. If you have a device which can work properly
> from 1.5V down to 0.9V, then it would use the entire range of an
> alkaline battery and you should still get more runtime out of the
> alkaline than the NiMH. I think that the only way that an NiMH could
> deliver a longer runtime would be if the device were only able to
> operate below 1.3V or if it were much more efficient from 1.3V to 0.9V
> than it is from 1.5V to 1.3V.
>
> Sean

Please take a look at this page, specifically the chart in the middle  
to see what I'm talking about. Depending on the minimum voltage for  
your application, there can be quite a bit more area under the curve  
of the NiMH cell that is above the minimum line.

-Pete
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