Method and Apparatus for Estimating Battery Capacity of a Battery

A system for determining a battery capacity for a vehicle battery comprising:

• a battery;
• at least one component for drawing power from the battery;
• a voltmeter for measuring an open circuit voltage of the battery at ignition start sequences;
• a current sensor for sensing current drawn from the battery;
• and
• a control module for determining a battery parameter for the vehicle battery that is a function of a present open circuit voltage measurement for a present ignition startup, a function of at least one open circuit voltage observation of a previous ignition startup, a function of a current draw integration over a time period from a previous ignition startup event to a present ignition startup event, and a function of an adjustment factor, the control module further determining a battery parameter based on a new battery, the control module calculating the battery capacity as function of the battery parameter for the vehicle battery and a function of the battery parameter for the new battery.

The system of claim 11 wherein the control module estimating a battery parameter for the vehicle battery is represented by the following formula:

• θ
• ^
• k
• =
• λ
• θ
• 
• θ
• ^
• k
• -
• 1
• +
• (
• 1
• -
• λ
• θ
• )
• 
• V
• oc
• 
• (
• t
• k
• )
• -
• V
• ^
• oc
• 
• (
• t
• k
• -
• 1
• )
• ∫
• t
• k
• -
• 1
• t
• k
• 
• I
• 
• 
• t
• where λθ{circumflex over (θ)}k-1 is the previous battery parameter observation and
• V
• oc
• 
• (
• t
• k
• )
• -
• V
• ^
• oc
• 
• (
• t
• k
• -
• 1
• )
• ∫
• t
• k
• -
• 1
• t
• k
• 
• I
• 
• 
• t
• a current battery parameter observation, where Voc (t) is the present open circuit voltage measurement at a kth ignition start, {circumflex over (V)}oc (tk-1) is a previous open circuit voltage observation, {circumflex over (θ)}k-1 is the battery parameter of the vehicle battery estimated at a previous ignition start, I is a current draw from the vehicle battery, and λθ is an adjustment factor.