Patent ID: 7674551

Claim:
A state of charge indicator for a battery having a liquid electrolyte comprising: a viewing rod having an observation surface at a first end, a conical reflection surface at a second end, and a generally cylindrical outer surface intermediate the first end and the second end, the viewing rod including a central longitudinal axis; a ball cage coupled to the second end of the viewing rod through which the electrolyte can flow; at least one ball guide channel provided in the ball cage and arranged obliquely with respect to the central longitudinal axis such that an upper portion of the ball guide channel extends upward from the conical reflection surface and a lower portion of the ball guide channel extends downward from the conical reflection surface, the upper portion of the ball guide channel including an upper boundary surface adjacent the conical reflection surface; and at least one ball provided in the ball guide channel; wherein the upper boundary surface of the upper portion of the ball guide channel extends upward from and above the conical reflection surface such that it is smoothly connected to the conical reflection surface and is generally co-linear with the conical reflection surface on a guide line; and wherein the at least one ball is configured to move upward toward the upper portion when the density of the electrolyte increases: and wherein a distance between the upper boundary surface and the conical reflection surface is less than ¼ of the diameter of the ball provided in the ball guide channel.