Sealey professional battery drop tester 6 12v polarity free sealey bt91 7pf american style drop tester polarity protected cables impossible to damage unit by misconnection load applied by internal switchgear no sparking suitable for 6 and 12volt batteries applies load across cells and measures output on meter accurate indication of battery voltage faulty cell and short circuited cell sealey bt91 7pf professional battery drop tester 6 12v polarity free