after new batteries & altnatial my car only start sometime help

YOU COULD POSS HAVE A BAD STARTER ASSM! CADILAC LIKES TO PUT STARTER UNDER INTAKE SO IT GETS HEAT SOAKED AND THE DESERT ISN'T VERY NICE TO ELECTRICAL PARTS HERE IN TOWN

if the anti-theft light is on..... you can try a relearn process first... turn key to "on", leave for 30 min. exactly turn key to off for 10 min exactly. repeat 2 more times. then remove key from ignition. let sit about 30 sec to a min. then try to start. if that doesn't work try to clean the metal ends, both sides, visable on key with a small nail file, using the not so rough side. lightly run across metal portion about 3 times. this cleans the contacts allowing the elec signal to be sent fully to start car. it worked for me, tried on first set of keys, worked. tried spare key w/o doing the filing and it didn't work. filed and it started. been working everyday, all day for last 3 months. hope it works for you, will keep about $150-$200 in your pocket.

I am having the same issue