Between 2 batboxes you can just use copper insulated wire, but it may be easier to just place them adjacent to each other. The trick is to make sure that their ouputs are facing the right way. The side that is different from the other 5 is the output. Ideally you should connect the output of one batbox directly to an input side of another. What kind of power source are you connecting them to? It seems to me that could be your problem, because batbox output is 32 eu/t and I don't know anything that explodes at that power level.