Adam Funk:
You are absolutely correct about open circuit testing of batteries is
useless.... many otherwise almost dead batteries will have a surprisingly
high open circuit terminal voltage......
.....BUT the test LOAD (car headlamp) that you are using is not much more
than a dead short compared to the design capabilities of the 9V battery.
These batteries were designed with practical average load currents of 20ma
and occassionally will be found in devices using 100ma or possibly a little
more.
A good and practical load that I have used for actual evaluation and
comparison with other 9volt batteries of questionable freshness is a 270 ohm
, 1 watt resistor, which gives a load current of about 33ma.... this will
"test" the battery terminal voltage with a suitable load and will not ruin
or drain the battery while doing it.
Best Regards,
Daniel Sofie
Electronics Supply & Repair
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"Adam Funk" wrote in message
...

I was under the impression that the open-circuit voltage wasn't a
reliable measure of how much "juice" is left in a battery.