An internal impedance of a battery (30) is automatically determined by operating a processor (13) to analyze current flowing through the battery to determine if a transient condition due to change of current is occurring and determining when the transient condition has ended. A voltage of the battery is measured while a steady current is being supplied by the battery. The present depth of discharge (DOD) of the battery is determined and a database is accessed to determine a corresponding value of open circuit voltage. The internal impedance is computed by dividing the difference between the measured voltage of the battery and the open circuit voltage at the present DOD by an average value of the steady current. A remaining run-time of the battery can be determined using a total zero-current capacity of the battery, integrating the current to determine a net transfer of charge from the battery, determining a value of total run-time that would be required to reduce the voltage of the battery to a predetermined lower limit, determining the duration of the integrating, and determining the remaining run-time by subtracting the duration of the integrating from the total run-time.

Title
Circuit and method for determining battery impedance increase with aging
Application Number
10/428659
Publication Number
20040128089
Application Date
May 2, 2003
Publication Date
July 1, 2004
Inventor
David L Freeman
McKinley
TX, US
Dan R Poole
Austin
TX, US
Evgenij Barsoukov
Dallas
TX, US
Agent
Cahill Von Hellens & Glazer
AZ, US
Agent
Charles R Hoffman
AZ, US
IPC
G06F 19/00
View Original Source