You can feel lower voltages if you fingers are injured, or if you... lick them. As kids (6-9y) we used to test the voltages of 3R12 (4.5v) by touching the pole

You can feel lower voltages if you fingers are injured, or if you... lick them. As kids (6-9y) we used to test the voltages of 3R12 (4.5v) by touching the poles with tongue, a sharp bites - the battery was good.