EBay jumper cable looking battery charger

Just bought a battery charger from EBay, without looking at the picture on my phone. When it arrived it was 6 feet of heavy duty small cables, with battery clamps, and the other end had a cigarette lighter or accessory plug. Said the charger was for m/c, marine batterys, etc. I have an accessory plug-in but it's accross the pos. and neg. and if I plug this in to charge my old 4-5 amp battery it seems like it'd really short it out. Just connecting it like pos. to neg. pretty much to the old battery. Does it work like that? Because I need the extra battery on there eventually but read it needs a switch that doesn't arc when you switch batterys. Anybody explain this, mostly the battery charger and using it for a similar battery. Thanks