"Bruce W.1" wrote in message ...
Say for a NiCad or NiMH battery, how is battery capacity calculated?
Say I put a resistor across the battery and measured the voltage
periodically. Is it the area of the curve above 1.1 volts, 0.9 volts,
or what?

Usually they pick a voltage that lets you get some large percentage of
the total available energy. I think 1.0V is OK for a NiCd, though you
could be more conservative and use 1.1V. There probably isn't much
energy left by the time you reach a volt, at least at modest current.
It also makes a difference what rate you discharge. So for a 500mA-H
cell, if you discharge at 50mA, that's a "ten hour rate" and would be
a common way to rate the cell. If your application draws heavier
current, you'd be advised to test at that current, and you will find
the mA-H value to be lower than at the lower rate.

I'd think you could find lots of info on the web about this, since
it's a common topic. I've seen quite a few articles in various trade
journals about it.

Cheers,
Tom