A water refilling plug for automatically filling battery cells has a cylindrical plug housing that includes a connector fitting for water delivery into a housing, as well as a valve, actuated by a float, having an annular valve body and a conical valve seat. The valve is arranged between an inflow channel and an outflow channel leading into the battery cell. In accordance with the invention, swirl-generating deflection channels are arranged between the annular inflow channel and the conical valve seat in a pattern distributed over a circumference in the plug.