IN SITU BATTERY TESTER

1 . A battery tester for testing a battery under test installed in a device without requiring direct access to or removal of the battery under test, comprising:

a stereo plug configured for insertion into a stereo jack on the device to thereby complete a circuit including the battery under test and a load circuit in the device to which the battery under test supplies power;

first circuitry configured to measure a battery voltage corresponding to the battery under test;

second circuitry configured to measure a load current corresponding to the load circuit to which the battery under test supplies power;

control circuitry configured to generate one or more signals representative of remaining battery life for the battery under test with reference to the battery voltage and the load current; and

a display configured to generate a representation of the remaining battery life using the one or more signals.

2 . The battery tester of claim 1 wherein the display comprises a digital display having a plurality of characters.

3 . The battery tester of claim 2 wherein the representation of the remaining battery life comprises one or both of a voltage or a number of hours.

4 . The battery tester of claim 1 wherein the display comprises a plurality of light emitting diodes, and wherein the representation of the remaining battery life comprises one or more colors generated by the light emitting diodes.

5 . The battery tester of claim 1 further comprising a housing containing the first circuitry, the second circuitry, and the control circuitry, and on which the display is mounted, the battery tester further comprising two contacts external to the housing and in electrical communication with fourth circuitry, the two contacts and the fourth circuitry being configured for testing of a first type of loose battery connected to the contacts.

6 . The battery tester of claim 5 wherein the fourth circuitry is further configured for testing of at least one additional type of loose battery connected to one of the contacts and a tip conductor of the stereo plug.

7 . The battery tester of claim 1 wherein the first circuitry comprises a high impedance voltage divider, and wherein the control circuitry includes an analog-to-digital converter having an input range, the battery tester further comprising ranging circuitry configured to adapt the battery voltage to the input range of the analog-to-digital converter.

8 . The battery tester of claim 1 wherein the second circuitry employs a sense resistance comprising a combination of one or more of a plurality of sense resistors to measure the load current, and wherein the second circuitry further comprises selection circuitry configured to select from among the sense resistors for different ranges of a current signal generated by the sense resistance.

9 . The battery tester of claim 1 further comprising third circuitry configured to select a battery chemistry type, wherein the control circuitry is further configured to generate the one or more signals representative of remaining battery life with reference to the battery chemistry type selected.

10 . The battery tester of claim 9 wherein the third circuitry comprises switching circuitry configured to select from among a plurality of battery chemistry types, the plurality of battery chemistry types comprising two or more of alkaline, carbon-zinc, or rechargeable.

11 . The battery tester of claim 1 wherein the stereo plug comprises a first tip conductor, a first ring conductor, and a first sleeve conductor configured to contact a second tip conductor, a second ring conductor, and a second sleeve conductor in the stereo jack, respectively, wherein the stereo plug has a profile that makes it unlikely that short circuits will occur between respective ones of the second tip conductor, the second ring conductor, and the second sleeve conductor as the stereo plug is being inserted into the stereo jack.

12 . The battery tester of claim 1 further comprising internal battery test circuitry configured to measure a second voltage associated with an internal battery for powering the battery tester.

13 . The battery tester of claim 1 further comprising plug test circuitry configured to measure a second voltage representative of conductivity of the stereo plug.

14 . The battery tester of claim 1 wherein the control circuitry comprises a microcontroller programmed to control operation of the first and second circuitry and the display.

15 . The battery tester of claim 14 wherein the microcontroller employs a representation of the battery voltage as an index into a lookup table to select a current*time value, and generates the one or more signals representative of remaining battery life by dividing the current*time value by a representation of the load current.

16 . The battery tester of claim 15 further comprising third circuitry configured to select a battery chemistry type, wherein the lookup table is one of a plurality of lookup tables each of which corresponds to a particular battery chemistry type, the microcontroller being further configured to select the lookup table from among the plurality of lookup tables with reference to the battery chemistry type selected.

17 . The battery tester of claim 15 wherein the microcontroller is further configured to compensate for reduction of the remaining battery life as a function of increasing current draw.

18 . The battery tester of claim 15 wherein the microcontroller is further configured to compensate for the remaining battery life occurring at a lower battery voltage relative to the measured battery voltage.

19 . A stereo plug for insertion into a stereo jack, comprising a tip conductor, a ring conductor, and a sleeve conductor, wherein the stereo plug has a profile such that the tip conductor is narrower than a maximum width of the widest portion of the stereo plug, and wherein the ring conductor is also narrower than the maximum width of the stereo plug, and wherein the stereo plug further comprises a first dielectric insulator insulating the tip conductor from the ring conductor, and a second dielectric insulator insulating the ring conductor from the sleeve conductor, a portion of the first dielectric insulator increasing in width from the tip conductor to the maximum width and then decreasing in width from the maximum width to the ring conductor, a portion of the second dielectric insulator increasing in width from the ring conductor to the maximum width.