I often suspect that they are selling seconds.
Stewart
At 08:31 PM 2/21/2010, you wrote:
Voltage is voltage, and the right voltage is needed. But 7.4 V
compared to 7.2 V is small. One may wonder how a battery can differ
by a small voltage, since a battery by definition is a series of
electrical cells with voltages that add up from the individual cells
that are connected in series. For commercial usage, there are only
a few kinds of cells (i.e., chemistry) available, and each kind has
a unique voltage associated with it within a narrow tolerance. I
suspect the difference between a 7.4 V battery and a 7.2 volt
battery is simply a kind of puffery used to describe the battery
since your camera will probably require one kind of electrical
cell: usually today, a lithium-ion or perhaps a nickel metal
hydride cell. (Check your camera manual to see which kind is recommended.)
The mAh means "milliamp-hours" and measures the charge that may be
contained in a fully charged cell or battery. (The charge is also
measured in Coulombs.) Ideally, a 650 mAh battery will deliver 650
milliamps of current for one hour before becoming discharged -- or
325 milliamps for two hours, etc. Thus, a higher mAh rating ought
to mean that the battery will have a longer life in a device before
needing to be recharged.
But as the battery ages, both the energy stored and the voltage are
subject to diminish after many recharges. Eventually the battery
becomes unsuitable for your application and needs to be replaced.
So far I have gotten good results by ordering from Battery Engine, a
web store. It is not the cheapest but offers a good discount from
the manufacturer's list price. There surely are other good sources,
but I have not had good results from eBay, especially those that
ship from Hong Kong at a wonderfully low price.
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