Temperature dependent charge algorithm

1. A method for charging a rechargeable battery comprising:

obtaining, by charging circuitry, an open circuit voltage of the battery prior to a charging session, the charging circuitry in electrical communication with a power source and the battery;

initiating, by the charging circuitry, the charging session to charge the battery at a constant charge current-constant charge voltage with power provided from the power source, the charging session corresponding to one of a first charging strategy or a second charging strategy based on the obtained open circuit voltage of the battery;

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

obtaining, by the charging circuitry, a charge termination time (t t ) based on the ambient temperature (T); and

terminating, by the charging circuitry, the charging session when the charge termination time (t t ) is reached; and

when the charging session corresponds to the first charging strategy:

initiating, by the charging circuitry, a timer (t) when the charging session to charge the battery at the constant charge current-constant charge voltage initiates; and

when a voltage (V bat ) of the battery reaches a predetermined voltage after initiating the charging session:

obtaining, by the charging circuitry, the ambient temperature (T) and a polarization time (t p ), the polarization time (t p ) corresponding to a value of the timer (t) from when the charging session initiates until the battery voltage (V bat ) reaches the predetermined voltage; and

estimating, by the charging circuitry, the charge termination time (t t ) as a function of the ambient temperature (T), the polarization time (t p ), the charge current, and the charge voltage.

2. The method of claim 1 , wherein the charging session corresponds to the first charging strategy when the obtained battery open circuit voltage is less than a voltage threshold and the charging session corresponds to the second charging strategy when the obtained battery open circuit voltage is greater than the voltage threshold.

3. The method of claim 1 , further comprising terminating, by the charging circuitry, the charging session if the battery voltage (V bat ) does not reach the predetermined voltage within a polarization time threshold and the battery voltage (V bat ) is less than a termination voltage threshold.

4. The method of claim 1 , wherein the predetermined voltage corresponds to one of a peak polarization voltage (V PP ) or a predetermined voltage value near the peak polarization voltage (V PP ).

5. The method of claim 1 , further comprising, after the voltage (V bat ) of the battery reaches the predetermined voltage:

continuing to charge the battery at the constant charge current-constant charge voltage until the battery voltage (V bat ) reaches a voltage limit, the voltage limit corresponding to a maximum battery voltage (V bat_max );

decreasing, by the charging circuitry, the charge current at a rate when the battery voltage (V bat ) reaches the voltage limit; and

terminating the charging session upon the earlier one of the timer (t) reaching the charge termination time (t t ) or the charge current falling below a charge current threshold.

6. The method of claim 1 , wherein obtaining the charge termination time (t t ) when the charging session corresponds to the second charging strategy comprises:

initiating, by the charging circuitry, a timer (t) when the charging session initiates;

obtaining the ambient temperature (T) when the timer (t) reaches an initial charging time; and

estimating, by the charging circuitry, the charge termination time (t t ) and an end of charge current as a function of the ambient temperature (T), the charge current, and the charge voltage.

7. The method of claim 6 , further comprising, after the timer (t) reaches the initial charging time:

continuing to charge the battery at the constant charge current-constant charge voltage until the battery voltage (V bat ) reaches a voltage limit, the voltage limit corresponding to a maximum battery voltage (V bat_max );

decreasing, by the charging circuitry, the charge current at a rate when the battery voltage (V bat ) reaches the voltage limit; and

terminating the charging session upon the earlier one of the timer (t) reaching the charge termination time (t t ) or the charge current falling below the end of charge current for a current termination period.

8. The method of claim 6 , further comprising, after the timer (t) and the charging session initiate, terminating, by the charging circuitry, the charging session if the charge current falls below a charge current threshold within the initial charging time.

9. The method of claim 1 , wherein the battery comprises a silver-zinc battery type.

10. The method of claim 1 , wherein the battery comprises a single cell or two or more cells in series, and wherein the charging circuitry is implemented upon a silicon chip.

11. An apparatus for charging a rechargeable battery comprising:

a temperature sensor configured to measure ambient temperature (T); and

charging circuitry in electrical communication with the temperature sensor, the battery, and a power source, the charging circuitry configured to:

initiate a charging session to charge the battery at a constant charge current to a maximum battery voltage (V bat_max ) with power provided from the power source;

obtain the ambient temperature (T) from the temperature sensor;

obtain a charge termination time (t t ) based on the ambient temperature (T); and

terminate the charging session when the charge termination time (t t ) is reached; and

wherein, according to a first charging strategy, the charging circuitry is further configured to:

obtain an open circuit voltage of the battery prior to initiating the charging session;

determine the battery is indicative of being in a lower voltage plateau prior to initiating the charging session when the battery open circuit voltage is less than a voltage threshold;

obtain the ambient temperature (T) and a polarization time (t p ) when a voltage (V bat ) of the battery under load reaches a predetermined voltage after initiating the charging session, the polarization time (t p ) corresponding to a time from when the charging session initiates until the battery voltage (V bat ) reaches the predetermined voltage; and

estimate the charge termination time (t t ) as a function of the ambient temperature (T) and the polarization time (t p ).

12. The apparatus of claim 11 , wherein the charging circuitry is further configured to:

after the battery voltage (V bat ) reaches the predetermined voltage, continue charging the battery at the constant charge current until the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max );

decrease the charge current at a rate when the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max ); and

terminate the charging session upon the earlier one of the charge termination time (t t ) or the charge current falling below a charge current threshold.

13. The apparatus of claim 11 , wherein the predetermined voltage corresponds to one of a peak polarization voltage (V PP ) or a predetermined voltage value near the peak polarization voltage (V PP ).

14. The apparatus of claim 11 , wherein, according to a second charging strategy, the charging circuitry is further configured to:

obtain an open circuit voltage of the battery prior to initiating the charging session;

determine the battery is indicative of being in an upper voltage plateau prior ( 210 ) to initiating the charging session when the battery open circuit voltage is greater than a voltage threshold;

initiate a timer (t) when the charging session initiates;

obtain the ambient temperature (T) when the timer (t) reaches an initial charging time; and

estimate the charge termination time (t t ) and an end of charge current as a function of the ambient temperature (T).

15. The apparatus of claim 14 , wherein the charging circuitry is further configured to:

after the timer (t) reaches the initial charging time, continue charging the battery at the constant charge current until the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max );

decrease the charge current at a rate when the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max ); and

terminate the charging session upon the earlier one of the timer (t) reaching the charge termination time (t t ) or the charge current falling below the end of charge current for a current termination period.

16. The apparatus of claim 14 , wherein the charging circuitry is further configured to terminate the charging session if the charge current falls below a charge current threshold within the initial charging time.

17. The apparatus of claim 11 , wherein the battery comprises a single cell or two or more cells in series having a silver-zinc battery type.

18. The apparatus of claim 11 , further comprising a silicon chip implementing the charging circuitry and the temperature sensor.

19. The apparatus of claim 18 , wherein the silicon chip is located in a device powered by the battery.

20. The apparatus of claim 18 , wherein the silicon chip is located in a charging base, the charging base configured to electrically connect to the battery and the power source.

21. A charging system comprising:

a rechargeable battery configured to provide power to electrical components of a device;

a power source; and

a charger comprising charging circuitry in electrical communication with the power source and the battery when the battery is docked with the charging circuitry, the charging circuitry:

obtaining an open circuit voltage of the battery prior to a charging session when the battery is docked with the charging circuitry;

initiating the charging session to charge the battery at a constant charge current to a maximum battery voltage (V bat_max ) with power provided from the power source, the charging session corresponding to one of a first charging strategy or a second charging strategy based on the obtained battery open circuit voltage;

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

obtaining a charge termination time (t t ) based on the ambient temperature (T); and

terminating the charging session when the charge termination time (t t ) is reached; and

wherein the charging circuitry obtains the charge termination time (t t ) according to the first charging strategy by:

determining the battery is indicative of being in a lower voltage plateau prior to initiating the charging session when the battery open circuit voltage is less than a voltage threshold;

obtaining the ambient temperature (T) and a polarization time (t p ) when a voltage (V bat ) of the battery under load reaches a predetermined voltage after initiating the charging session, the polarization time (t p ) corresponding to a time from when the charging session initiates until the battery voltage (V bat ) reaches the predetermined voltage; and

estimating the charge termination time (t t ) as a function of the ambient temperature (T) and the polarization time (t p ).

22. The system of claim 21 , wherein the charging circuitry terminates the charging session by:

after the battery voltage (V bat ) reaches the predetermined voltage, continuing to charge the battery at the constant charge current until the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max );

decreasing the charge current at a rate when the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max ); and

terminating the charging session upon the earlier one of the charge termination time (t t ) or the charge current falling below a charge current threshold.

23. The system of claim 21 , wherein the charging circuitry obtains the charge termination time (t t ) according to the second charging strategy by:

determining the battery is indicative of being in an upper voltage plateau prior to initiating the charging session when the battery open circuit voltage is greater than a voltage threshold;

initiating a timer (t) when the charging session initiates;

obtaining the ambient temperature (T) when the timer (t) reaches an initial charging time; and

estimating the charge termination time (t t ) and an end of charge current as a function of the ambient temperature (T).

24. The system of claim 23 , wherein the charging circuitry terminates the charging session by:

after the timer (t) reaches the initial charging time, continuing to charge the battery at the constant charge current until the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max );

decreasing the charge current at a rate when the battery voltage (V bat ) reaches the maximum battery voltage (V bat_max ); and

terminating the charging session upon the earlier one of the timer (t) reaching the charge termination time (t t ) or the charge current falling below the end of charge current for a current termination period.

25. The system of claim 21 , wherein the battery comprises a silver-zinc battery type and the battery-powered device comprises a hearing aid device.

26. The system of claim 21 , wherein the charging circuitry is located within the battery-powered device or a charging base external to the battery-powered device.