Battery charger with temperature compensation

1. A method for controlling battery charging, said method comprising:

comparing a battery temperature with an environmental temperature;

charging the battery in a normal charge state at a normal charge rate if the battery temperature is greater than the environmental temperature beginning at a transition to a positive temperature difference;

charging the battery in a warm charge state at a charge rate faster than the normal charge rate if the battery temperature is not greater than the environmental temperature beginning at a transition to a negative temperature difference;

monitoring a difference between the battery temperature and the environmental temperature when charging in the warm charge state; and

switching from the warm charge state to the normal charge state when the difference between the battery temperature and the environmental temperature is within a predetermined range.

2. A method in accordance with claim 1 further comprising terminating charging of the battery in the normal charge state when a temperature gradient increase of the battery temperature exceeds a predetermined threshold.

3. A method in accordance with claim 1 wherein the predetermined range is between about one degree Celsius and about three degrees Celsius.

4. A method in accordance with claim 1 further comprising providing to a charge controller the higher of the battery temperature and the environmental temperature.

5. A method in accordance with claim 1 wherein the charging is performed using an in-vehicle charger.

6. A method in accordance with claim 1 wherein the battery is configured to power a land mobile radio.

7. A method in accordance with claim 1 further comprising sensing the environmental temperature using a temperature sensing device of a battery charger.

8. A method in accordance with claim 1 wherein the monitoring is performed one of continuously and periodically.

9. A method in accordance with claim 1 further comprising terminating charging of the battery based on a predetermined temperature gradient threshold and wherein the terminating only occurs in the normal charge state.

10. A charge monitor for a battery charger, said charge monitor comprising:

an environmental temperature sensor configured to monitor an environmental temperature;

a comparator configured to compare the environmental temperature with a battery temperature from a battery temperature sensor of a battery being charged to determine a higher of the environmental temperature and battery temperature; and

a charge controller receiving the determined higher temperature and configured to operate in a normal charge state at a normal charge rate if the battery temperature is greater than the environmental temperature beginning at a transition to a positive temperature difference, and to operate in a warm charge state at a charge rate faster than the normal charge rate if the battery temperature is not greater than the environmental temperature beginning at a transition to a negative temperature difference, and wherein charging is switched from the warm charge state to the normal charge state when the difference between the battery temperature and the environmental temperature is within a predetermined range.

11. A charge monitor in accordance with claim 10 further comprising a multiplexer for switching an input to the charge controller between the sensed battery temperature and the sensed environmental temperature.

12. A charge monitor in accordance with claim 11 wherein the multiplexer is configured to switch between the battery temperature sensor and the environmental temperature sensor based on which sensed temperature is higher.

13. A charge monitor in accordance with claim 10 wherein the charge controller is configured to terminate charging in the normal charge state when a temperature gradient increase of the battery temperature exceeds a predetermined threshold.

14. A charge monitor in accordance with claim 10 wherein each of the battery temperature sensor and the environmental temperature sensor is configured to periodically measure temperature.

15. A charge monitor in accordance with claim 10 wherein each of the battery temperature sensor and the environmental temperature sensor is configured to continuously measure temperature.

16. A battery charger comprising:

an interface for connection to a battery to be charged; and

a charge monitor having a comparator configured to compare a sensed battery temperature with a sensed environmental temperature and a charge controller configured to operate in a normal charge state at a normal charge rate if the battery temperature is greater than the environmental temperature beginning at a transition to a positive temperature difference, and to operate in a warm charge state at a charge rate faster than the normal charge rate if the battery temperature is not greater than the environmental temperature beginning at a transition to a negative temperature difference, and wherein charging is switched from the warm charge state to the normal charge state when the difference between the battery temperature and the environmental temperature is within a predetermined range.

17. A battery charger in accordance with claim 16 wherein the interface is configured to engage a land mobile radio battery.

18. A battery charger in accordance with claim 16 further comprising memory configured to store sensed temperature information.

19. A battery charger in accordance with claim 16 wherein the charge monitor comprises a multiplexer for switching between a sensed battery temperature and a sensed environmental temperature.

20. A battery charger in accordance with claim 16 wherein the charge monitor is configured to terminate battery charging only in the normal charge state based on a predetermined temperature gradient threshold.