Patent ID: 8193771

Claim:
A combination electronic device having an internal battery mounted within said electronic device, an internal circuit contained within said electronic device, and a stereo-type audio output jack, and a battery tester for use in testing the charge level of said internal battery; wherein the stereo-type audio output jack has a first contact connected to a terminal of the internal battery, wherein the other terminal of said battery is connected to deliver operating power to said circuit contained within said electronic device, wherein the stereo-type audio output jack has a second contact connected to an output of said circuit, and a third contact connected to said circuit and connectible to deliver operating power from the first contact to said circuit through a connection made from said first contact to said third contact by a conductive part of an audio plug inserted into said stereo-type audio output jack; and wherein the battery tester comprises a plug insertable into said stereo-type audio output jack, said plug having at least two coaxial, cylindrical, and longitudinally spaced, conductors two of said cylindrical conductors being isolated from each other and connectible respectively to said first and third contacts, and a battery charge measuring device connected by said two of said cylindrical conductors to said first and third contacts.