Wayne S. posted some comments on SR44 size, silver oxide cells for OM's, along
with a few old threads:
>I test my batteries on occasion, using a resistance load (5-10K ohm)
and compare it to the open circuit voltage to get an idea of the
internal resistance.
<<
A more telling test would be to use a load of around 80-100 Ohm which is about
what the camera looks like at shutter release (and approx what the self test
load is). This loads the cell up to about 14-18mA.(~1.4V/100 = 14mA) A 100
Ohm 1/4w resistor is a very easy to get part from Radio-Shack or a surplus
store. Do the test quickly as cell polarization will drop voltage over the
time.of test, and shutter current pulses are normally short. Check the OM4
service manual specs on Mark's website, to get OM4 lock up voltage minimum
levels.
Some digital multi-meters have a battery test range that puts a small load on
the cell while checking voltage. I checked an old "Goldstar" multimeter and it
puts a load of 1kOhm on both its 9V and 1.5V test range. This is a light load
of ~1.5mA for the 357 but is better than nothing.
The 357 data sheet used to actually have a typical spec for deltaV for a
specified pulse width and load current. Unfortunately the manufacturers have
taken a lot of that kind of detailed information out of their data sheets now.
I tested a new unused Everready 357 cell with following result:
unloaded: 1.629V
using multi-meter battery test (1KOhm) 1.622V
with 100 Ohm Load for ~1 sec: 1.563V
This is approx (1.622-1.563)/(1.563/100-1.622/1000) = 4 Ohm, battery internal
resistance for the new cell. YMMV.
Regards,
Tim Hughes
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