I was having the same problem with my RDX not starting with a good battery and good alternator. Luckily I’m friends with a Honda/Acura Master Tech and he was able to track down a parasitic draw that he has encountered many times before. Turns out the relay for the A/C condenser shorts out and drains the battery without the key in it and when it’s just sitting. I believe it was a 30amp grey fuse(square box type unlike conventional fuses) located near kick panel near drivers side foot area. It was an inexpensive fix and I haven’t had a problem since. Hope this helps-sorry I don’t have the part number or pics.