To answer your question, the max current being equal is irrelevant. The voltage determines what the current through your body will be, even though as others have suggested, you can still be in trouble at 30VDC given "ideal?" conditions.
The generally accepted danger from electrocution in the ranges you are talking about is current flowing across the thorax, inducing ventricular fibrillation. The current required to do that is depending on the person 30 - 100 mA to 200 mA. As for "across the brain...." I know of the odd ECT patient that has been through quite a few beneficial currents in the region!!!
Just as a side note, a "D" cell would practically need to have electrodes connected to each side of the heart to induce VF....