I have a 2500 GMC crew cab and I went out today to start it and nothing happened on 2013 Chevrolet Silverado 2500 HD

I tried to start it and totally dead. Battery is fine but the electronic gauges where dancing all over the place even thou I didn't have the key in the ignition. I could hear the juice from the battery drawing juice so I disconnected the battery. Does this mean that the computer brain is going dead? Please help!!!

Asked by for the 2013 Chevrolet Silverado 2500 HD