Low temperature  (-20 to -40 C) characteristics regarding drop in
capacity as a percentage of nominal capacity of Nimh batteries

Hi,

The characteristics seem to vary from one manufacturer to other. I am
including the analysis of two major brands below:


You can find detailed characteristics of Energizer NiMH batteries at:

http://data.energizer.com/batteryinfo/application_manuals/nickel_metal_hydride.htm

As seen in the Figure 12, discharge capacity highly varies with the
temperature. It goes about %20 of its nominal capacity at -20 degrees
Celcius. Quoting the site: "Use of nickel metal hydride cells in cold
environments may force significant capacity derating from
room-temperature values."


However, the data sheet for Panasonic NiMH batteries are somewhat
different:

http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiMH_Overview.pdf

As you can see in "Discharge temperature characteristics" figure in
page 5 (second figure in the left column), the capacity ratio is about
60% at -20 degrees Celcius (when charged at the recommended constant
charging current).


Search strategy:
Searched Google for:
nickel metal hydride temperature discharge-capacity


Hope this helps
Regards
Bio