1994 Buick le sabre issue

I would start by putting a meter between the battery post and the battery cable (+ post) because there is a drain you should get some reading. Now with the help of another person, start pulling fuses until the meter reading changes.....do all the fuses just incase there are more than one drain. You would expect the radio to have a drain as it keeps the correct time. Once you find the circuit, figure out what is on that circuit and start disconnecting things until you find the problem