Re: Any insights about eventual rechargeable LiION AA batteries?

This next round of tests was for Lithium AA's. First we tried the
Chinese AA's lithiums that had given reasonable operation at room
temperature. At -20C they would not turn on the transmitter. Not good.

The next trial was with the Eveready lithium at -20 C and that battery
ran for 4 hours and 12 minutes which is pretty good at -20 C (-4F).
The second trial was at -30 C (-22F) and the battery lasted 2:50
another good result. The final run on the Eveready's was after cold
soaking the battery for 5 hours. That result was 2:41 very close to
the 20 mnute soak test. Remember, the NiMh batteries did not like
being cold soaked more than part of an hour and failed after a 2 hour
soak. Also remember that the batteries reach final temperature in 15
minutes or less in the cold chamber.

Conclusion:
NiMh batteries will work if put in the transmitter without a long cold
soak even down to -30C.
Eveready lithiums are the way to go at low temperatures.
LarryF
Lectro


On Fri, 05 May 2006 10:53:09 -0600, Larry Fisher
<fisherlarry@xxxxxxxxx> wrote:

More intriguing results now that the temp chamber is repaired. The
batteries do get down to the final temperature in 15 minutes or less
of cold soaking. In that time, the battery had gotten down to within 1
degree of the chamber setting. The temperature didn't change at all
when the circulating air was shut off indicating the temperature was
the same, all through the battery. The thermocouple was held against
the battery with several wraps of tape.

So the NiMh batteries will run at -30 C (Eveready, Sanyo, maybe
others) but only if they have been at that temperature for a short
period of time. Two hours of cold soaking reduces the run time to 15%
of normal; 12 hours of cold soaking is a big fat 0%. So if you take a
battery from a warm pocket, put it in a cold unit and operate it
within 15 minutes, you can get 50% of normal battery life. YMMV
LarryF
Lectro

On Thu, 04 May 2006 12:36:43 -0600, Larry Fisher
<fisherlarry@xxxxxxxxx> wrote:

The first Eveready 2200 mAh ran for 1 hour and 54 minutes. It had been
cold soaked in the chamber for 20 minutes by laying it horizontaly up
against a wall. That way two cold metal surfaces contacted the battery
and the fan blew cold air over the battery. The reason I mention all
this is I was pretty sure the battery was fully cold soaked. However,
a battery that I cold soaked for 12 hours wouldn't even start the
transmitter. It is possible that 20 minutes isn't enough to fully cool
the battery so I will have to put a temperature probe on a battery to
check that out. I have read that the longer the NiMh batteries are
kept cold, the poorer their performance and that may be what is
happening. (???)
.

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