Storage batteries connected in series in an uninterruptable or back-up power supply system may have voltage potential differences between exposed terminals or conductors that exceed safety limits. A demountable insulating shield having apertures may be positioned so that the series string may be broken into a plurality of series sub-strings having a lesser potential difference has a cover over the aperture through which the series string configuration may be connected and disconnected. The cover may he an insulating material removably fastened to the insulating shield or a sliding cover that is captivated to the insulating shield. When the series string has been divided in to the sub-strings, the insulating shield may be demounted from the structure housing the batteries so that the batteries or their connections may be serviced.