Help! 2007C6 dead from electrical problems

Long story-short--car has had electrical problems from day one-drive it and ok but after parking, battery goes dead. Car is an automatic so reverse parking not an issue. Like an idiot, I placed a battery tender on it instead of going to dealer at the start and it solved problemsfor several months . Several weeks ago, after not being on tender for several days it was totally dead-tried to charge with tender and in process put cables on the wrong poles-ie positive on negative and vice versa for only several seconds but.....called dealer--car hauled to dealership and new battery was put in. Vette ran ok with new battery then-Two days later, car was dead but a new message appeared on message center-"Service Charging System" Dealer has been great during this whole process but here is where we are now---two weeks later--they have replaced battery, alternator, ECM,BCM, and ignition switch. Car runs 15 -20 miles, Service Charging System light comes, car goes back into garage and dies.
The car has had modifications to exhaust and intake systems and now getting some comments about no more warranty coverage although these mods have nothing to do with electrical problems--that talk from factory rep, not from the dealer and I am concerned that if they don't come up with an answer soon ,I'm going to be SOL. Any help from you guys would be appreciated especially if someone out their has had similar problems with a C6. I am not mechanically inclined and as a retired banker know nothing about a cars electrical system so I will be passing any worth while information back to my service manager who has been super to me in this process---it helps when he has model Corvettes and pictures of vettes all over his office..........
thank you for any ideas.