James said:
I recently purchased charger which came with a set of Nickel Metal
Hydride AA batteries. I notice the batteries are rated at 1.2 volts,
whereas regular alkaline batteries are 1.5 volts.
Why the difference in voltage? And will some devices have inferior
performance with NiMH due to the lower voltage?
Technically, what you're talking about is a "cell," not
a "battery," although common usage IS certainly to call
all such things "batteries." But this is one case where the
difference is important.
A "cell" is the smallest unit of an electrochemical source
that will produce power - i.e., it is the basic unit of construction
for "batteries" (which are arrays of multiple cells, generally in
series), and it has one each "positive" plate and "negative"
plate. The voltage you get across a single cell depends on
the particular chemistry in question. For instance, the lead-acid
batteries you have in your car provide about 2.1 volts per cell,
so a six cell battery actually has a nominal unloaded voltage,
at full charge, of about 12.6 volts. The good old carbon-zinc
"dry" cells that used to be the norm in flashlights and such,
as well as the more recently developed "alkaline" types,
provide 1.5 volts/cell. And, as you've discovered, nickel
metal hydride (NiMH) cells give you about 1.2 volts/cell,
nominal.
Some devices intended for the carbon-zinc or standard alkaline
types may, in fact, have trouble with the lower cell voltage;
hopefully, they'll tell you this in the operator's manual, and
advise that you not use the NiMH or other lower-voltage types.
And others will have no problem at all.
Bob M.
