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NiMH in cold weather

I ran some tests with NiMH in the freezer and fridge today. NiCad would be better I guess but they're pretty nasty environment-wise.

I found a few discussions about NiMH from different sources.

Cold Weather Battery Performance: NIMH vs. Lithium from a photographers' forum.

Some interesting replies:
"I use 1300 mAH NiMH batteries in my EOS 3 power booster. In December at Bosque I shot 15-20 rolls per day, with battery-sucking 500/4.5 and 300/4 IS lenses at 6 FPS and AI Servo AF mode. Typically it would go above freezing as the day progressed, but it started out very cold, probably below 20 F.

I wouldn't hesitate to use NiMH batteries in the cold, so long as you can recharge them each day."

"At -4 degrees F both NIMH AA and Lithium CR5 batteries are down to 1/2 normal capacities. At 32 degrees F both are down to between 90% - 95% of capacity. Alkaline AA cells are down to 65% at 32 degrees F and useless at -4 F. "

"I am in North Dakota and shot the lunar eclipse last month in -12F temperatures using a 2CR5 battery in my ElanIIe. It was subjected to these temperatures for over 3 hours and I still had power to shoot to the end."

NiMH reduced performance in cold weather from an EV forum

Replies:
"It´s because of the chemistriy of NiMh-Batteries. The internal resistance of the batteries becomes higher at temperatures below 0°C so they "seem" to be empty earlier. Onother problem is that the batteries which are "hit" by very cold cooling-air "seem" to be empty earlier than the other warmer ones."

"I've red on a RC forum here in Holland that NiMH behave like this:

15-30 degrees Celsius (100% SoC)
10 degrees Celsius it is 80%
0 degrees Celsius it is only 60%
-10 degrees Celsius it is only 15%!!"

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