NEED HELP and SOLUTION quick...Battery....??

I recently moved my batt. to the bed...used 2 gauge welding cable...anyways...i drove it today for the first time...did fine...i was at work, went to go home...turned over, batt. died...went and got a new battery...put it on, the thing kept sparking...went to start it...battery starting smoking and fried....ANY IDEAS ON WHAT THE PROB. COULD BE........

crossed cable? i had the samething happen when i relocated. found i had a short in my fuse box under the hood. goodluck electrical is a pain in the ass.