Bought the neighbors 1999 Chevy Lumina. 140,000 miles. All we knew about it was that the alternator was replaced over the last year. The battery drained and we ended up needing to replace the ignition switch (it was letting the key out in aux, thus the drained battery). Then had to get new keys, as the security system was wiped out. We bought a new battery and had the brakes fixed completely. The dealer did the ignition repair and security restart and new keys. Then we had our mechanic fix the brakes and fluids, but while he was doing this he said the battery drained out, and he had to recharge it. So he replaced the battery as well. All is fine, we take it home and drive it that weekend (this is a car for our 16 year old son). We leave it a week and it is dead. The mechanic recharged the (new) battery, did a parasitic draw test, and found nothing.
Something is drawing the life from the battery. What could it be???
Check to make sure the glove box light (if equipped) and the trunk light both are going off when the lids are closed. (easiest to check when dark)
After the mechanic did all that work, did he do a load test on the charging system?