Battery charging method and system depending on ambient temperature

1. A method for charging a rechargeable battery comprising:

estimating an initial state of charge of the battery (SOC 0 );

determining whether the initial state of charge of the battery (SOC 0 ) is greater than a threshold state of charge (SOC X );

when the initial state of charge of the battery (SOC 0 ) is less than or equal to the threshold state of charge (SOC X ), initiating a first charging strategy for charging the battery, the first charging strategy comprises charging, by charging circuitry, the battery at a temperature-independent constant charge voltage (CV XT ) and at a first current (I 1 ) with power provided from a power source in electrical communication with the charging circuitry; and

when the initial state of charge of the battery (SOC 0 ) is greater than a threshold state of charge (SOC X ), initiating a second charging strategy for charging the battery, the second charging strategy comprising:

obtaining an environmental temperature (T E ) measured by a temperature sensor in communication with the charging circuitry;

calculating a temperature-based constant charge voltage (CV T ) based on the environmental temperature (T E ); and

charging, by the charging circuitry, the battery at the temperature-based constant charge voltage (CV T ) and at a second current (I 2 ) with power provided from the power source.

2. The method of claim 1 , wherein the second charging strategy further comprises:

calculating an end termination current (I end ) as a function of the environmental temperature (T E ); and

terminating the charging of the battery when the second current (I 2 ) is less than the end termination current (I end ).

3. The method of claim 2 , wherein the second charging strategy further comprises:

determining if the second current (I 2 ) is decreasing over time; and

terminating the charging of the battery when the second current (I 2 ) is decreasing over time and is less than the end termination current (T end ).

4. The method of claim 1 , wherein the first charging strategy further comprises:

calculating a max termination current (I max ) as a function of the environmental temperature (T E ) and the initial state of charge (SOC 0 ); and

terminating the charging of the battery when the first current (I 1 ) is less than or equal to the max termination current (I max ).

5. The method of claim 4 , wherein the first charging strategy further comprises:

setting a target capacity (Q tgt );

determining a capacity (Q) of the battery; and

terminating the charging of the battery when the first current (I 1 ) is less than or equal to the max termination current (I max ) and the battery capacity (Q) is at least the target capacity (Q tgt ).

6. The method of claim 1 , wherein the first charging strategy further comprises:

redetecting battery voltage (V batt ) and changing to the second charging strategy if V batt is above a threshold voltage.

7. The method of claim 1 , wherein the second charging strategy further comprises:

calculating a running average of battery voltages over a time (t ave ) and changing to the first charging strategy if the running average of battery voltages is less than a threshold average voltage at t ave .

8. The method of claim 1 , wherein the first charging strategy further comprises:

detecting a battery chemistry error by charging the battery to a threshold voltage, pausing charging to allow the battery voltage to relax down to about the open circuit voltage (OCV) of the battery, and determining if the OCV is below a threshold OCV.

9. The method of claim 1 , wherein the threshold state of charge (SOC X ) is selected from a percentage between about 25% and about 75% of the battery's capacity.

10. The method of claim 1 , wherein the threshold state of charge (SOC X ) is selected from a percentage between about 40% and about 60% of the battery's capacity.

11. The method of claim 1 , further comprising measuring a time to polarization (t p ) of the battery, wherein the initial state of charge (SOC 0 ) is estimated as a function of the time to polarization (t p ).

12. The method of claim 1 , wherein the initial state of charge (SOC 0 ) is estimated as a function of battery voltage (V batt ).

13. The method of claim 1 , wherein the value of the temperature-based constant charge voltage (CV T ) is bounded by a predetermined minimum charge voltage and a predetermined maximum charge voltage.

14. The method of claim 1 , wherein the environmental temperature (T E ) is obtained periodically.

15. The method of claim 1 , wherein the rechargeable battery comprises a silver-zinc battery.

16. The method of claim 1 , wherein the rechargeable battery comprises a single cell.

17. The method of claim 1 , wherein the rechargeable battery comprises two or more cells in series.

18. The method of claim 1 , wherein the charging circuitry is implemented upon a silicon chip.