Methods and apparatus for measuring battery characteristics

1. An apparatus for determining a state of health of a battery selectively coupled to a charger and a load, comprising:

a fuel gauge circuit, coupled to the battery and communicatively coupled to the charger and the load, configured to:

measure a remaining capacity of the battery during a first open state;

determine a first voltage according to the remaining capacity;

prime the battery by sequentially:

charging the battery during a first time period by selectively coupling the charger to the battery;

creating a second open state during a second time period by disconnecting both the charger and the load from the battery; and

discharging the battery during a third time period by selectively coupling the load to the battery;

measure a voltage change from the first voltage during the third time period;

compute an aged resistance based on the change in voltage; and

compute the state of health of the battery based on the aged resistance and a set of battery characteristic data.

2. The apparatus according to claim 1 , wherein the fuel gauge circuit is further configured to prime the battery by:

measuring an actual voltage during the second open state; and

comparing the actual voltage with the first voltage, during the second open state.

3. The apparatus according to claim 1 , wherein the fuel gauge circuit is further configured to:

measure a second voltage during the first open state; and

measure a third voltage during the third time period.

4. The apparatus according to claim 3 , wherein the change in voltage is the difference between the first voltage and the third voltage.

5. The apparatus according to claim 3 , wherein:

the fuel gauge circuit is further configured to compare the first voltage and the second voltage; and

the fuel gauge primes the battery if the first voltage is greater than the second voltage.

6. The apparatus according to claim 1 , wherein the set of battery characteristic data comprises:

a relationship between an original resistance and the remaining capacity; and

an original capacity.

7. The apparatus according to claim 1 , wherein the fuel gauge circuit is further configured to:

measure a current through the battery during the third time period; and

compute the aged resistance by dividing the change in voltage by the measured current.

8. The apparatus according to claim 1 , wherein the fuel gauge circuit is further configured to:

compute a resistance ratio, wherein the resistance ratio is equal to the aged resistance divided by an original resistance;

determine an aged capacity based on the computed resistance ratio; and

compute the state of health based on the aged capacity and an original capacity.

9. A method for determining a state of health of a battery selectively coupled to a charger and a load, comprising:

measuring a remaining capacity during a first open state;

determining an expected battery voltage according to the measured remaining capacity;

priming the battery by sequentially:

charging the battery during a first time period;

creating a second open state during a second time period by disconnecting both the charger and the load from the battery; and

discharging the battery during a third time period;

measuring a voltage change from the expected battery voltage during the third time period;

computing an aged resistance based on the measured change in voltage; and

computing the state of health of the battery based on the computed aged resistance and a set of battery characteristic data.

10. The method for determining a state of health of a battery according to claim 9 , wherein priming the battery further comprises:

measuring an actual battery voltage during the second open state; and

comparing the actual voltage with the expected voltage, during the second open state.

11. The method for determining a state of health of a battery according to claim 9 , further comprising:

measuring a current through the battery during the third time period;

computing a resistance ratio based on the aged resistance; and

determining an aged capacity based on the resistance ratio.

12. The method for determining a state of health of a battery according to claim 11 wherein computing the state of health of the battery comprises dividing the aged capacity by an original capacity.

13. The method for determining a state of health of a battery according to claim 9 , wherein the set of battery characteristic data comprises:

an original resistance versus remaining capacity; and

an original capacity.

14. The method for determining a state of health of a battery according to claim 9 , further comprising:

measuring a second battery voltage during the first open state;

comparing the expected battery voltage and the second battery voltage; and

priming the battery if the second battery voltage is less than the expected battery voltage.

15. A system capable of monitoring a battery and battery characteristics, comprising:

a switchable charger configured to be selectively coupled to the battery;

a switchable load configured to be selectively coupled to the battery;

a fuel gauge circuit, configured to be coupled to the battery, and communicatively coupled to the switchable charger and the switchable load, wherein the fuel gauge circuit is configured to:

measure a remaining capacity of the battery during a first open state;

determine expected battery characteristic data according to the measured remaining capacity;

prime the battery by sequentially:

charging the battery during a first time period by selectively coupling the charger to the battery;

creating a second open state during a second time period by disconnecting both the charger and the load from the battery; and

discharging the battery during a third time period by selectively coupling the load to the battery;

determine a change in voltage of the battery based on at least a portion of the expected battery characteristic data;

measure a current during the third time period;

compute an aged resistance of the battery according to the determined change in voltage and the measured current;

compute a resistance ratio according to the aged resistance;

determine an aged capacity based on the computed resistance ratio;

compute a state of health value based on the computed aged capacity and an original capacity.

16. The system according to claim 15 , wherein the expected battery characteristic data comprises:

an expected first voltage; and

an original resistance.

17. The system according to claim 16 , wherein the fuel gauge circuit is further configured to:

measure an actual second voltage during the first open state;

compare the expected first voltage and the actual second voltage;

prime the battery if the actual second voltage is less than the expected first voltage;

measure an actual third voltage during the third time period; and

measure a current through the battery during the third time period.

18. The system according to claim 16 , wherein:

the resistance ratio is equal to the aged resistance divided by the original resistance; and

the state of health value is equal to the aged capacity divided by the original capacity.

19. The system according to claim 16 , wherein the fuel gauge circuit is further configured to prime the battery by:

measuring an actual voltage during the second open state; and

comparing the measured actual voltage with the expected first voltage.

20. The system according to claim 15 , wherein the first, second, and third time periods are predetermined.