METHODS AND APPARATUS FOR A BATTERY

1 . A management circuit connected to a battery comprising:

a voltage sensor responsive to an output voltage of the battery;

a current sensor responsive to a current of the battery;

a secondary current circuit coupled to the current sensor and configured to generate a first current and a second current,

wherein each of the first and second currents produce a change in the current of the battery and a change in the output voltage of the battery; and

a logic unit responsive to the voltage sensor and the current sensor, wherein the logic unit is configured to:

compute the change in the output voltage according to the first current and second currents; and

compute an aged internal resistance of the battery according to the change in output voltage and at least one of first and second currents.

2 . The management circuit according to claim 1 , further comprising:

a memory device responsive to the logic unit and adapted to store:

a first battery characteristics indicating a relationship between the output voltage and a relative state of charge of the battery; and

a second battery characteristics indicating a relationship between an internal resistance and the relative state of charge of the battery.

3 . The management circuit according to claim 2 , wherein the logic unit is configured to determine a baseline internal resistance of the battery according to the relative state of charge of the battery and the second battery characteristics.

4 . The management circuit according to claim 2 , wherein the baseline internal resistance is an internal resistance of the battery when the battery is new.

5 . The management circuit according to claim 2 , wherein the second battery characteristic data further comprises predetermined data describing an internal resistance of the battery as the battery ages.

6 . The management circuit according to claim 1 , wherein the secondary current circuit comprises a first transistor connected in parallel with a second transistor, wherein each of the first and second transistors comprise a gate terminal.

7 . The management circuit according to claim 6 , wherein the secondary current circuit further comprises a voltage source circuit to adapted to selectively apply a voltage to the gate terminals of the first and second transistors.

8 . The management circuit according to claim 1 , further comprising a temperature sensor coupled to the logic unit and responsive to a temperature of the battery, wherein the logic unit is configured to adjust the aged internal resistance of the battery according to the temperature of the battery.

9 . A method for determining an aging characteristic of a battery comprising:

measuring a relative state of charge of the battery;

extracting a baseline internal resistance value from a set of battery data based on the measured relative state of charge;

measuring an output voltage of the battery;

measuring a current of the battery, wherein the current is purposefully influenced by a secondary current;

calculating an aged internal resistance of the battery based on the measured current and the measured output voltage.

10 . The method of claim 9 , further comprising: estimating the state of health of the battery based on the calculated aged internal resistance and the baseline internal resistance of the battery.

11 . The method of claim 9 , further comprising generating the secondary current, wherein generating the secondary current comprises applying a voltage to a transistor connected to a positive terminal of the battery.

12 . The method of claim 9 , further comprising:

measuring a temperature of the battery; and

adjusting the aged internal resistance based on the temperature.

13 . A system for a battery, comprising:

a voltage sensor responsive to an output voltage of the battery;

a memory device storing:

predetermined first battery characteristic data indicating a relationship between the output voltage and a relative state of charge of the battery;

predetermined second battery characteristic data indicating a relationship between a baseline internal resistance and the relative state of charge of the battery;

a current sensor responsive to a current of the battery;

a logic unit responsive to the voltage sensor and the current sensor and having access to the memory device, wherein the logic unit is adapted to:

determine a baseline internal resistance of the battery; and

compute an aged internal resistance of the battery; and

a display unit coupled to the logic unit and adapted to display an indicator related to a state of health of the battery based on the computed aged internal resistance.

14 . The system according to claim 13 , wherein the logic unit determines the baseline internal resistance of the battery based on the second battery characteristic data.

15 . The system according to claim 14 , wherein the baseline internal resistance is an internal resistance of the battery when the battery is new.

16 . The system according to claim 13 , further comprising a temperature sensor coupled to the logic unit and responsive to a temperature of the battery, wherein the logic unit is configured to adjust the aged internal resistance of the battery according to the temperature of the battery.

17 . The system according to claim 13 , wherein the second battery characteristic data further comprises predetermined data describing an internal resistance of the battery as the battery ages.

18 . The system according to claim 13 , further comprising:

a secondary current circuit coupled to the current sensor and comprising:

a first transistor;

a second transistor connected in parallel with the first transistor; and

a voltage source circuit connected to a gate terminal of each of the first and second transistors.

19 . The system according to claim 18 , wherein the voltage source circuit applies a predetermined voltage to each gate terminal of the first and second transistors.

20 . The system according to claim 13 , wherein the logic unit computes the aged internal resistance based on the output voltage and the current of the battery.