A state of charge indicator for a battery having a liquid electrolyte includes 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 includes a central longitudinal axis. The state of charge indicator also includes a ball cage coupled to the second end of the viewing rod through which the electrolyte can flow and at least one ball guide channel provided in the ball cage and arranged obliquely with respect to the central longitudinal axis. The ball guide channel includes an upper boundary surface adjacent the conical reflection surface. The upper boundary surface is smoothly connected to the conical reflection surface.