To shorten the electrolyte filling time and to continuously provide batteries of stable performance by reducing the pressure of an battery jar inside by a preliminary pressure reduction bath preliminarily reducing the pressure of the battery jar in filling the electrolyte in the battery jar after storing a pole plate group in the battery jar, switching a switch valve connecting the preliminary pressure reduction bath to a trap bath of the electrolyte, and by communicating the battery jar with the trap bath.

In filling electrolyte using an electrolyte quantitative feeder 1, a pole plate group is mounted on a cylinder after storing it in a battery jar B, the cylinder 7 is raised, and a pad in the tip of a nozzle is brought in contact with an opening part of the battery jar B. Then, a switch valve 4 is switched, a preliminary pressure reduction bath 6 preliminarily reducing the pressure by a vacuum pump 5 is communicated with a space in the battery jar, and the pressure inside the battery jar B is reduced. In this case, a two-way switch valve communicating the preliminary pressure reduction bath 6 with the vacuum pump 5 may be closed. After that, the switch valve 4 is switched, a trap bath 3 and the battery jar B inside are communicated together, and the trap bath 3 and the electrolyte L accumulated to a prescribed quantity are conducted by the pressure difference.