Better to test with a current (or amp) meter to check for the actual current being drawn with everything "off". Disconnect one cable from the battery then clip the ammeter between the cable and the terminal on the battery it came off of. Problem is in modern vehicles, not everything turns off, there are clocks, memory power for radios, the ECU, etc. and who knows what else pulling small amounts of currnet. Typical draws are in the 20-30 mA range (0.020 - 0.030 amps). If you get much over that, then something is probably wrong. As stated, pull fuses until the current flow drops, then figure out what things are powered via that fuse and check out each item. A good battery can probably take a 30mA drain for 2-4 weeks w/o trouble. A bad battery might not handle that overnight.