Really dumb question, did you CLEAN THE CONNECTIONS at the battery? Helped a guy stranded in a boat that would only click. We jumped it with a good battery from my boat and still clicked. He put my battery in his boat and it clicked. I asked him if he cleaned the terminals and his reply was yes they are tight. After an hour I said, humor me and disconnect the battery, use your knife and clean as best you can the posts and terminals and give that a try. He insisted that the connections were good. Again I ask him to clean the connections to shiny metal and he gave in and did it. Guess what? Tight connections arent always a good connection. A pocket knife solved the problem in this case. Just a suggestion.