Car want start battery drain

I HAVE A 99 CADILLAC DEVILLE IT IS NOT FULLY LOADED…IF I DONT START IT IN 1 TO 3 DAYS ITS BATTERY IS COMPLETELY DEAD AFTERMARKET DVD WAS DISCONNECTED AND IT STILL WENT DEAD…I HAVE A NEW BATTERY AND AN OLD ONE THEY BOTH ARE TESTED GOOD AND IT STILL GOES DEAD…I AM TIRED OF PLUGGING IT INTO TRICKLE CHARGER