On Tue, 27 Nov 2012 07:21:09 -0500, Bill Petersen
wrote:

I purchased three solar spot lights from Walmart this past summer. As of
this time, two of them have nearly died and only one is still shining
brightly. I can assume it's the battery. Inside, the two larger
spotlights have a Westinghouse 3.2V 400 mA LiFePO4 cell. I'd like to
replace this battery with something better. What are my alternatives?
Weather here varies from about 80-90 F during Summertime down to
freezing during the Winter. Thanks for your help. Bill

Dunno. You can somewhat predict the useful life of the battery in
days by estimating the number of charger/discharge cycles.
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
At 90F, my guess(tm) is that you're probably good for about 300
charge/discharge cycles, which is about a year.

While only one factor, trying to charge and remain charged at 100%
capacity while hot is the magic formula for killing LiIon batteries.
I suggest using a larger capacity LiIon battery, and that will never
fully charge, thus extending the battery life. Also, make an effort
to keep it cool, such as painting it white or reflective. You'll
never use or need the full capacity of the battery, so your lights
should work fairly normally.

Another idea is to use supercaps. You'll need a fairly large number
depending on load. They're also rather expensive and bulky. However,
they last for millions of charge/discharge cycles.
http://batteryuniversity.com/learn/article/whats_the_role_of_the_supercapacitor


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Jeff Liebermann
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Santa Cruz CA 95060 http://802.11junk.com
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