Was going along at about 4500rpm's when the TAC quit, went to 0. Thought maybe a loose connection. Fished for a couple hours, attempted to start engine and the battery was completely dead. Got a tow. Battery was 4 years old so I bought a new starting battery and she cranked right up. Next morning went to start boat and battery was totally dead again. I disconnected all accessories from the starting battery and recharged with only the engine hooked up, same thing. What is happening????