System and method for calculating a state of charge of a battery

1. A method, comprising:

determining a first state of charge of a battery;

determining a rate of change of the state of charge of the battery, the rate of change being determined based on a charge current being supplied to the battery; and

determining an updated state of charge as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the updated state of charge.

2. The method of claim 1 , further comprising:

displaying the updated state of charge.

3. The method of claim 1 , wherein the first state of charge is determined based on an open circuit battery voltage.

4. The method of claim 1 , wherein the first state of charge is determined based on information received from a calculation of the state of charge during the discharging of the battery.

5. The method of claim 1 , wherein at least two measurements of charge current are used to determine the rate of change.

6. The method of claim 5 , wherein, when a first of the at least two measurements of charge current is substantially equal to a fast charge current, the rate of change is determined based on the following formula,

ROC=100×(I old +I new )/(2 ×C ×60),

where ROC is the rate of change, I old is the first of the at least two measurements of charge current, I new is a second of the at least two measurements of charge current and C a capacity of the battery.

7. The method of claim 5 , wherein, when a first of the at least two measurements of charge current is less than a fast charge current, a ratio of a second of the at least two measurements of charge current to the first of the at least two measurements of charge current is determined.

8. The method of claim 7 , wherein, when the ratio is less than 1, the rate of change is determined based on the following formula,

ROC=(100−SOC old )/TTT

where ROC is the rate of change, SOC old is the present state of charge and TTT is a time to terminate charging.

9. The method of claim 8 , wherein the TTT is incremented by a predetermined value when the second of the at least two measurements multiplied by the ratio is greater than a charge termination current.

10. The method of claim 1 , wherein measuring the charge current is performed one of periodically and non-periodically.

11. The method of claim 2 , wherein the updated state of charge is displayed as a percentage of a capacity of the battery.

12. A system, comprising:

a current sensor measuring a charge current being supplied to a rechargeable battery;

a processor calculating a first state of charge of the rechargeable battery and calculating a rate of change of a state of charge of the rechargeable battery based on the charge current, the processor calculating an updated state of charge of the rechargeable battery as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the undated state of charge.

13. The system of claim 12 , further comprising:

a voltage sensor measuring a voltage of the battery prior to a start of a charging operation, wherein the voltage is used by the processor to calculate the state of charge prior to the start of the charging operation.

14. The system of claim 12 , further comprising:

a display displaying the updated state of charge.

15. The system of claim 12 , further comprising:

a memory storing the charge current.

16. The system of claim 12 , wherein the rechargeable battery is a lithium ion battery.

17. The system of claim 12 , wherein at least two measurements of charge current are used to determine the rate of change.

18. The system of claim 17 , wherein, when a first of the at least two measurements of charge current is substantially equal to a fast charge current, the rate of change is determined based on the following formula,

ROC=100×(I old +I new )/(2 ×C ×60),

where ROC is the rate of change, I old is the first of the at least two measurements of charge current, I new is a second of the at least two measurements of charge current and C a capacity of the battery.

19. The system of claim 17 , wherein, when a first of the at least two measurements of charge current is less than a fast charge current, a ratio of a second of the at least two measurements of charge current to the first of the at least two measurements of charge current is determined.

20. The system of claim 19 , wherein, when the ratio is less than 1, the rate of change is determined based on the following formula,

ROC=(100−SOC old )/TTT

where ROC is the rate of change, SOC old is the present state of charge and TTT is a time to terminate charging.

21. The system of claim 20 , wherein the TTT is incremented by a predetermined value when the second of the at least two measurements multiplied by the ratio is greater than a charge termination current.

22. A device, comprising:

current measuring means for measuring a charge current being supplied to a rechargeable battery;

calculating means for calculating a first state of charge of the rechargeable battery;

calculating means for calculating a rate of change of a state of charge of the rechargeable battery based on the charge current, the calculating means calculating an updated state of charge of the rechargeable battery as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the updated state of charge.

23. A computer readable storage medium including a set of instructions executable by a processor, the set of instructions operable to:

determine a first state of charge of a battery;

receive an indication of a charge current being supplied to the battery;

determine a rate of change of the state of charge of the battery, the rate of change being determined based on the indication of the charge current; and

determine an updated state of charge as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the updated state of charge.