A bad battery would 'drain' itself without any current flowing thru the cables. You have actual current draw going on.

Over 100 mA is definitely a drain. I only asked, just in case the actual drain was 5mA (clock & stereo memory) then a bad battery would be a good possibility.

An alarm system is always a good suspect, but I don't know enough to help you with that.

You've already proven that it's 'downstream' of the 100A main fuse, so probably it's just going to be some incredibly tedious process of tracing wires. Leave the 100A fuse in, take out all the other fuses & relays, & search the car for ANY wire that's still live.