Importance

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Abstract

The invention relates to apparatus for determining the state of charge of electric storage batteries. The apparatus makes use of known quiescent battery (16) terminal voltage recovery characteristics after a prior energy transfer to predict the ultimate steady state terminal voltage as a measure of state of charge. In one embodiment, this is accomplished by using a voltage-controlled oscillator (18) and a reversible counter (20) to measure a first battery (16) terminal voltage over a fixed time interval, storing that measurement in a register (24), measuring a second terminal voltage by reversing the counter (24) and counting the counter down for an identical fixed interval of time, and then determining the slope of the voltage recovery (at) (26) (30) based upon the difference between the two voltage measurements as evidenced by the count remaining in the counter (20) and adding a factor (at) (74) to the first voltage measurement based upon the voltage difference measurement to determine a predicted steady state voltage as an indication (28) of the charge on the battery.

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First Claim