What's the best way to track down what's draining the battery???
"A few days" says the current drain is fairly small, so I would start by doing some checking with a DMM that includes a 10 or 20 amp scale. The procedure varies with the meter, but usually there is a special plug that is only used for the high current scale. Don't forget to move the lead back when you are done! (The high current input is basically a calibrated short to ground, so unpleasant things happen if you forget and try to check voltage with the lead in the current plug.)
To check current, you need to break the circuit and insert the meter (so the circuit closes through the meter). For example, to check that the alternator output is not the problem, you could pull that heavy black wire off the solenoid post, connect one meter lead to the black wire and the other lead to the solenoid post. With a digital meter you don't need to worry about polarity.
Another approach, simpler but much slower, is to try disconnecting portions of the car and wait to see if the battery still runs down. Although not common, it is possible to have things that only draw current some times, so this may be the only way to find the problem.
Just for example, I once had a non-LBC that would run the battery down overnight, but only sometimes. More by luck than anything, I finally realized that the relay for the rear window defogger grid had gotten contaminated with salt. On evenings when dew was forming, the combined moisture and salt would leak enough current to operate the relay coil and power up the grid! Never would have found that if I hadn't happened to walk by the car one night and see the indicator light on.