Deejay, I think, and hope, the actual current drawn would be a lot less than 4 amps - that is just the rating of the battery charger (incidentally the better 4 amp battery chargers have a thermal overload that limits their sustained output to 2.5 amps so the transformer won't burn out).
Quite small currents can cause substantial erosion. I once destroyed the bore of a near-new rifle's barrel by running electrolysis at 0.1 amps for about 15 hours. (Before someone asks, it was leaded up by using ill-fitting cast bullets, and it was alleged that the lead could be removed electrolytically.)
