My 06Fatboy has been sitting in the garage for months on a battery tender, I tried to start it and all I heard was a chatter sound, sounds like a machine gun when I hold the starter button down. Need help, thanks

Hi, I have been using the Harley Davidson Waterproof 800 Battery Tender on my 09 Fatboy for 6 months now without any problems. Recently I connected up and I noticed that the rear fender rail is 'live' when the tender is on. I have replaced the 'Pig Tail' harness but the issue is still present