"Jeff Liebermann"

Per a previous discussion, I decided to test whether new NiMH
batteries need to be conditioned or charged several times before
reaching their rated capacity. Apparently they do.

The test setup is a West Mtn Radio CBA-IIv1 battery analyzer.
http://802.11junk.com/jeffl/NiMH/cba-II.jpg
I didn't want to wait 20 hrs per test to get the official rated
capacity, so I elected to run the tests at 1C which resulted in about
a 45 minute test, but also resulted in a much lower capacity result.
It also caused some unexpected errors. The design of the CBA-II does
not include a Kelvin probe connection to eliminate any losses in the
cables and connectors. It measures the voltage at the load, instead
of at the battery. This is not a problem at low load currents, but at
2 amps, results in considerable error.

Two new (out of the package) batteries were used. An Energizer NiMH
2300 ma-hr cell, and a Duracell 2050 ma-hr cell. Between tests, the
batteries were quick charged in a Radio Shack 23-1305 NiMH quick
charger (15 min). Each battery was discharged 3 times and the
discharge curves plotted.

Note that the Energizer package says 2450 ma-hr, while the battery is
marked 2300 ma-hrs.
http://802.11junk.com/jeffl/NiMH/energizer.jpg

The Energizer cell showed no change in capacity between discharges.
http://802.11junk.com/jeffl/NiMH/Energizer-NiMH-2300.jpg
Using 1.0VDC as the end point, the measured cell capacity is:
Run 1 1785 ma-hr
Run 2 1890 ma-hr
Run 3 1895 ma-hr

The Duracell cell showed a larger change.
http://802.11junk.com/jeffl/NiMH/Duracelll-NiMH-2050.jpg
Using 1.0VDC as the end point, the measured cell capacity is:
Run 1 1200 ma-hr
Run 2 1270 ma-hr
Run 3 1385 ma-hr

The net improvement over 3 charge-discharge runs is about 10% for the
Energizer and 15% for the Duracell. Not huge, but certainly
measurable. Whether it is worth the effort conditioning the battery
before use, is debatable.


** You got something against NiMh cells ?

I would never mistreat NiMH AA cells the way you just have.

15 minute charging is absurd for any cell NOT designed for such abuse - it
causes overheating with new cells and destruction of older ones.

A 1C discharge test will never give the rated capacity figure with NiCd or
NiMH.

IME - the idea that new cells have a "running in "period is a MYTH
invented by retailers back in the 1970s when consumers were first sold AA
and C size NiCds and found their performance disappointing when compared to
alkalines.

The inherent lower terminal voltage and cell mAH capacity were the real
reasons.


..... Phil