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battery capacity

Subject: battery capacity
From: (Denise Thorpe)
Date: Tue, 5 Dec 95 13:51:49 PST
Richard said:

> I believe this experiment may be flawed. 


> A measurement of Specific Gravity 
> of the electrolyte is a more accurate measurement for "state of charge". 
> Unfortuately this number is a function of temperature, cell voltage is also a 
> function of temperature. 

The ambient temperature is absolutely constant here in San Diego; I'm still
driving around in shorts with my top down (the car's); so that's not a 
problem.  Maybe I'll dig out my electrolytic turkey baster battery tester
and test the battery with it.  The only problem is that I didn't test it
at the beginning so I have no trend data, but I can compare it to the 
non-identical battery sitting in the car that never moves.

> Battery voltage is a poor indication of charge, 
> the capacity will decrease much quicker.  The proof may be in a couple of 
> months when the battery is installed in a vehicle and the key is turned.  
> The voltage will then drop instantly to nothing.  

If cranking a car is the only real test of a battery's charge, then my
experiment would suffer from somebody-or-other's "uncertainty principle" 
since the test would affect the results.

> (all this worthless 
> knowledge came about from my electric Spitfire conversion project)

Did your conversion work?  I've always wanted to convert an MG 1100 to
an electric car.  There are so many places to stash batteries, like
under the front and back seats, under the false bottom in the trunk and
in all that space in the engine compartment.  Besides, I seem to have 
an excess of 1100's.

Denise Thorpe

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