Don't you think that more of the reason has to do with the fact that many
circuits require that the voltage not go much below 5V, so that you would
really need at least 6 V to start with to ensure that it stays above 5 for
the life of the battery?

You can approximate 5V fairly well with four NiCD cells (like what is used
for receiver packs in RC aircraft).

Also, IIRC, you cannot state that a particular chemistry gives exactly 3V,
for example, and you cannot do anything about it. I think it is a
logarithmic relationship with reagent concentration. In other words, you
COULD make a 5V lithium battery, but you would need insanely high solution
concentration, since the voltage goes as the log of the concentration. It's
sorta like saying that a silicon diode drop is 0.65 and you cannot do
anything about it. Actually you can, it depends on several things,
including dopant concentration, geometry of the diode, and the current
through it, but since they are all rather weak dependencies, it works out
that for practical values of these, you get a range of 0.5 to 0.8 volts.

Sean


At 09:54 PM 3/12/2003 -0500, you wrote:
> > Why don't they make 5V (or 2.5 V) batteries, with so many devices using
> > 5V logic?
>
>         Chemistry. A lithium cell outputs 3V, there is no way around it.
> Same as an
>alkaline cell outputs 1.5V and a NiCD cell outputs 1.2V. There is no way
>around it. TTYL
>
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