I finally get secondary batteries.... wire them together with double runs of 1/0.... then the 7/16 Craftsman wrench slips and falls across the + & - leads. Arc, Spark, and weld city. In about 1 second the wrench becomes a huge, super-heated fuse. No choice: grab it with hand and YANK the wrench off of the terminals. Yeah... likely battery damage, a big time scare, and a burn on my hand. F THAT!