Patent CA-2181415-A1 (CA)
Title: Battery charge indicator
Inventor: BOHMER WILLIAM
IPC: H01M10/48
Filed: 1996-07-17
Abstract: A battery charge indicator is disclosed which accurately displays the true state of charge or energy remaining in an alkaline battery in which the indicator is installed.  The indicator is responsive to a chemical reaction that has or has not occurred in the alkaline battery.  The indicator can detect partial discharges more accurately than the standard indicators or testers which use current or voltage to determine the condition of the battery.  The major component of an alkaline battery cell is the steel can.  The steel can contains the active chemical ingredients as well as being the conductive surface for the cathode which makes intimate contact against the inner surface of the can.  When the battery is sealed at the open end with a combination plug and anode, the closed end of the steel becomes very sensitive to internal pressures which are caused by the expansion of the cathode material due to electrical discharge of the battery and the hydrogen gas which accumulates during shelf life in storage.  Both of these phenomena cause a distortion or bulging of the closed end of the steel can, resulting in an overall increase in the height of the closed end of the can.  Even though the overall result is the same, there is a distinct difference between the distortion or bulge created by electrical discharge and the distortion or bulge created by hydrogen accumulation in storage.  When the battery is first manufactured, there is only a fractional amount of hydrogen gas present inside the steel can which result in none or very little distortion of the closed end of the steel can.  The increased amount of hydrogen during storage creates a distortion or bulge at the closed end of the battery with most of the bulge occurring in the center and with little or none present on the outer periphery.  When the battery has been electrically discharged, there is created additional pressure on the closed end of the battery.  This additional pressure generated by electrical discharge is substantial, since it is the result of the cathode material physically expanding inside the steel.  This causes distortion to extend to the outer periphery.  The angle between the surface of the closed end of the can at the periphery and the long end or wall of the battery becomes more than beyond ninety degrees.  When the battery is manufactured, the center surface and the periphery surface of the closed end of the battery can are flat.  When the battery has been in storage, the surface of the closed end assumes a bulge in the center due to accumulation of gas but remains flat on the perimeter surface.  The result is that the periphery surface remains perpendicular to the wall of the battery can even though there is distortion or bulge in the center of the closed end.  After the battery has been completely discharged, the surface of the closed end of the battery can is bulged or distorted in the center and the periphery surface.  The bulging of distortion on the closed end of the battery due to electrical discharge and the bulging or distortion due to outgasing can be distinguished by focusing on the perimeter surface of the closed end of the battery can.  The disclosed battery charge indicator utilizes the distortion or deflection of the periphery of the end portion of the can to move an indicating element to show the degree of discharge of the battery.