Russell McMahon
> 3.       A useful rule of thumb for determining the state of charge of a
> lead acid car battery is to subtract 11 Volt from the battery voltage and
> todivide the result by 0.028. The resultant figure is the approximate
> battery charge in percent.

So if we were to trust the figures from this page:

http://en.wikipedia.org/wiki/Lead-acid_battery#Voltages_for_common_usages

Open circuit voltage = 12.8V

12.8V - 11V = 1.8V
1.8V / 0.028 = 64.29%

This doesn't sound right. It assumes that at 100% charge, the battery 
voltage should be 13.8V.

What gives?

Vitaliy 

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