I have a 2001 jaq s-type about every 2 weeks the car won,t start new battery,it won.t let you jump it .i have to jump off alternator to get it to start,some one told me that it going into sleep mode,and won,t wake up.what is causing this .and when i go to the alternator its sending power back ,and waking it back up,but they didn,t know what causes this please help thanks