On Nov 16, 2009, at 9:44 AM, Vitaliy wrote:

> to keep the battery in good shape.

I have a number of those rechargeable emergency lights; things that  
plug into the wall, and turn on if the power goes off, and/or become  
flashlights.  Nice when they're needed; it gets very dark here when  
the power goes off.

Internally they have a NiCd battery (2*AA, usually) and some simple  
circuitry to keep the NiCd charged and detect outages.

I've recently been contemplating the thought that these would work  
better (as emergency lights) if the battery were NOT rechargeable.   
That is, it seems to me that the useful shelf life of a primary  
lithium battery is at least as long as the useful lifetime of a NiCd  
battery in anything but the most carefully designed continuous  
charging circuit.  Perhaps quite a bit longer (though comparing NiCd +  
circuitry of questionable quality and design (as tends to happen with  
mass-produced consumer items) with Lithium battery + circuitry of  
questionable quality makes it a pretty complex question...

The equation might change if you regularly use these as flashlights  
(but most make crappy flashlights.)

The latest versions of these lights claim to contain LiIon batteries  
(and uses LEDs.) I guess that solves some problems (especially with  
charging) and introduces others (what happened to that oft-rumored 2-y  
life of LiION cells (used or not.))

BillW

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