Systems, methods, and apparatus for battery charging

1. An apparatus comprising:

a rechargeable battery pack installed in an electric vehicle, the rechargeable battery pack coupled to a power supply, the power supply operable to provide a charge voltage to perform charging operations on the rechargeable battery pack;

a heating element to heat a fluid to be circulated through the rechargeable battery pack, the fluid thermally coupled to battery cells within the rechargeable battery pack;

a comparator circuit to compare a battery voltage of the rechargeable battery pack to a line source voltage coupled to inputs of the power supply, the comparator circuit operable to compare the battery voltage to the line source voltage and to provide an output signal when the battery voltage is less than a line voltage offset value, the line voltage offset value calculated based on a value added to a determined voltage level for the line source voltage; and

a control circuit coupled to receive the output signal of the comparator, and when a charge operation of the rechargeable battery pack is to be initiated, the control circuit is operable to couple the line source voltage to the power supply, wherein the control circuit is to couple the heating element in series between the line source voltage and the power supply when the comparator circuit is providing the output signal indicating that the battery voltage is less than the line voltage offset value, and to bypass the heating element if the comparator is not providing the output signal indicating that the battery voltage is less than the line voltage offset value.

2. The apparatus of claim 1 , wherein the comparator circuit is operable to monitor the battery voltage while the rechargeable battery pack is coupled to the heating element and the voltage source during a recharging operation, and to provide a bypass signal when the battery voltage exceeds a bypass threshold value, wherein the bypass threshold value is calculated based on the line voltage offset value; and

wherein the control circuit is coupled to receive the bypass signal and to bypass the heating element and continue the charging operation.

3. The apparatus of claim 1 , wherein the control circuit is operable to charge the rechargeable battery pack to one of a plurality of predetermined battery charge levels.

4. The apparatus of claim 1 , wherein the heating element, when coupled between the voltage source and the rechargeable battery pack, is coupled in series with the rechargeable battery pack to form a voltage divider for a voltage provided from the voltage source.

5. The apparatus of claim 1 , further including:

a temperature sensor coupled to the control circuit, the temperature sensor operable to monitor a temperature of the rechargeable battery pack and to provide a temperature value of the rechargeable battery pack; and

a cooling system operable to cool the fluid if the temperature value exceeds a threshold temperature while the heating element coupled between the voltage source and the rechargeable battery pack and is heating the fluid.

6. The apparatus of claim 1 , wherein the control circuit is operable to control a current provided by the voltage source to the rechargeable battery pack both when the heating element is coupled between the voltage source and the rechargeable battery pack and when the heating element is bypassed.

7. The apparatus of claim 1 , wherein the heating element includes a conductive metal wire.

8. The apparatus of claim 1 , wherein the heating element is located inside a tubing network, the tubing network operable to contain the fluid as the fluid circulates through the rechargeable battery pack.

9. The apparatus of claim 1 , wherein the battery cells are a plurality of 18650 form-factor lithium-ion cell.

10. A method comprising:

determining that a charge operation on a rechargeable battery pack is to be performed;

comparing a supply voltage to a battery voltage of the rechargeable battery pack to determine a line voltage offset value;

generating a charging voltage from the supply voltage; and

initiating charging of the rechargeable battery pack by coupling the charging voltage to the rechargeable battery pack, wherein coupling the charging voltage to the rechargeable battery pack includes coupling a heating element between the supply voltage and a set of power inputs to a power supply providing the charge voltage to the rechargeable battery pack when the battery voltage is less than a line voltage offset value, and bypassing the heating element when the battery voltage is not less than the line voltage offset value.

11. The method of claim 10 , further including:

circulating the fluid through the rechargeable battery pack during the charging while the heating element is coupled between the supply voltage and the set of power inputs to the power supply.

12. The method of claim 11 , further including:

monitoring a temperature of rechargeable battery pack, and

cooling the fluid circulating through the rechargeable battery pack when the monitored temperature exceeds a predetermined temperature level.

13. The method of claim 10 , further including:

comparing the supply voltage to the battery voltage while charging the rechargeable battery pack and having the heating element between the supply voltage and a set of power inputs to a power supply to determine if the battery voltage exceeds a bypass threshold value, wherein the bypass threshold value is calculated based on the line voltage offset value; and bypassing the heating element and continuing the charging when the battery voltage exceeds the bypass threshold value.

14. The method of claim 10 , wherein determining that a charge operation on a rechargeable battery pack is to be performed includes determining that the rechargeable battery pack is to be charged to one of a plurality of predetermined battery charge levels.

15. The method of claim 10 , further including:

controlling a current provided during the charging operation, both when the heating element is coupled between the supply voltage and a set of power inputs and when the heating element is bypassed.

16. The method of claim 10 , wherein generating a charging voltage from the supply voltage includes the supply voltage being an alternating current power source having a sinusoidal voltage waveform.

17. A system comprising:

a vehicle including a rechargeable battery pack, the rechargeable battery pack to provide at least a portion of the power used to propel the vehicle;

a heating element to heat a fluid to be circulated through the rechargeable battery pack, the fluid thermally coupled to battery cells within the rechargeable battery pack;

a charger operable to couple to a line source of electrical power and to detachably coupled to the vehicle, the charger to provide electrical power from the line source for performing charging operations of the rechargeable battery pack;

a comparator circuit to compare a battery voltage of the rechargeable battery pack to a line source voltage coupled to inputs of the power supply, the comparator circuit operable to compare the battery voltage to the line source voltage and to provide an output signal when the battery voltage is less than a line voltage offset value, the line voltage offset value calculated based on a value added to a determined voltage level for the line source voltage; and

a control circuit coupled to receive the output signal of the comparator, and when a charge operation of the rechargeable battery pack is to be initiated, the control circuit is operable to couple the line source voltage to the power supply, wherein the control circuit is to couple the heating element in series between the line source voltage and the power supply when the comparator circuit is providing the output signal indicating that the battery voltage is less than the line voltage offset value, and to bypass the heating element if the comparator is not providing the output signal indicating that the battery voltage is less than the line voltage offset value.

18. The system of claim 17 , wherein the comparator circuit is operable to monitor the battery voltage while the rechargeable battery pack is coupled to the heating element and the voltage source during a recharging operation, and to provide a bypass signal when the battery voltage exceeds a bypass threshold value, wherein the bypass threshold value is calculated based on the line voltage offset value; and

wherein the control circuit is coupled to receive the bypass signal and to bypass the heating element and continue the charging operation.

19. The system of claim 17 , wherein the control circuit is operable to charge the rechargeable battery pack to one of a plurality of predetermined battery charge levels.

20. The system of claim 17 , wherein the heating element, when coupled between the voltage source and the rechargeable battery pack, is coupled in series with the rechargeable battery pack to form a voltage divider for a voltage provided from the voltage source.