The fuse buddy tool employs the procedure Yamae described in his post # 5. The schematic rkw posted is helpful to identify the various circuits. As Yamae observed, an intermittent (random) voltage drain is the most difficult to isolate.

 

Good you tube videos on this. Testing voltage did not work for me but testing amps did. Disconnected the battery ground terminal, connect
Multimeter to the terminal and cable. Then pull fuses.

Also. Voltage regulator on alternator can be source of current lose. And ecm controls alternator charging on newer models, can cause variance in alternator charging rate that looks like alternator issue when is not. Detailed alternator tests are on you tube too