[Mickey#1]

I also suspect something is draining the battery. See if you can get your hands on a multimeter that can check DC amperage. Most meters have this capability. Disconnect the negative battery cable and set the meter to measure up to 10 amps. Place the black meter lead on the negative battery terminal & the red lead to the negative battery cable. The meter reading will spike a little then drop when the PCM goes into sleep mode. At this point the reading should be less than 1/10 amp. Everything needs to be off while doing this test. If the reading is to high you can pull fuses to isolate the circuit that is causing problems.