Apparatus and method for protecting a battery from overdischarge

1. A battery discharge indicator, comprising:

a positive connector configured to couple to a positive terminal of the battery;

a negative connector configured to couple to a negative terminal of the battery;

a voltage sensor configured to couple to the battery via the positive connector and the negative connector and to sense a battery terminal voltage; and

a microprocessor, coupled to the voltage sensor, configured to provide, substantially independently of a load being applied to the battery, a first alarm signal if a magnitude of the battery terminal voltage is below a first threshold voltage level for a first time interval and if the magnitude of the battery terminal voltage is below a second threshold voltage level for a second time interval.

2. The apparatus of claim 1 further comprising a temperature sensor configured to measure a battery temperature and to provide the measured battery temperature to the microprocessor, which in turn provides a second alarm signal if the battery temperature is above a predetermined threshold.

3. The apparatus of claim 2 wherein the measured battery temperature is the ambient temperature in close proximity to the battery.

4. The apparatus of claim 2 wherein the measured battery temperature is the external temperature of the battery.

5. The apparatus of claim 2 wherein the measured battery temperature in the internal temperature of the battery.

6. The apparatus of claim 2 wherein the temperature sensor comprises a non-contact infrared thermoplie sensor.

7. The apparatus of claim 2 wherein the temperature sensor comprises a thermocouple.

8. The apparatus of claim 2 wherein the temperature sensor comprises a resistance temperature detector (RTD) sensor.

9. The apparatus of claim 2 wherein the temperature sensor comprises an integrated circuit (IC) sensor.

10. The apparatus of claim 2 wherein the temperature sensor comprises a thermistor.

11. The apparatus of claim 1 wherein the first alarm signal is output as a visual alarm signal.

12. The apparatus of claim 1 wherein the first alarm signal is output as an audio alarm signal.

13. The apparatus of claim 1 further comprising an input, coupled to the microprocessor, configured to receive a selected one of a plurality of alarm signals, which the microprocessor is configured to employ as the first alarm signal.

14. The apparatus of claim 1 further comprising a voltage controller configured to receive an input voltage from the battery and to provide a substantially constant supply voltage to the microprocessor.

15. The apparatus of claim 14 wherein the voltage controller comprises a linear regulator.

16. The apparatus of claim 14 wherein the voltage controller comprises a switching regulator.

17. The apparatus of claim 14 wherein the voltage controller comprises a DC-DC converter.

18. The apparatus of claim 1 wherein the first threshold, voltage level is determined by the microprocessor by multiplying a predetermined cell threshold voltage value corresponding to a single cell of the battery by a number of cells in the battery.

19. A method of protecting a vehicle battery from overdischarge, comprising:

(a) sensing a battery voltage;

(b) providing a first alarm signal if a magnitude of the battery voltage is below a first threshold voltage level for a first interval of time; and

(c) providing the first alarm signal if the magnitude of the battery voltage is below a second threshold voltage level for a second interval of time,

wherein steps (b) and (c) are carried out substantially independently of a load being applied to the battery.

20. The method of claim 19 further comprising measuring a battery temperature and providing a second alarm signal if the measured battery temperature is above a predetermined threshold.