Multiple DTC's and Lost Communication after dead 12V

I went out to go to the store the other day and was met with a ton of error messages such as "Shift System Malfunctiom", "Braking Power Low", "Check Engine", "Secondary Collision Brake System Malfunction", " Brake Override Malfunction" and Drive-Start Control Malfunction". I was unable to shift the car to any gear and the car would not come to "Ready". The headlights started flashing and finally I could not open the back doors without overide or the rear hatch.

I hooked up my scanner and it recorded a multitude of codes including U029300, U1150, U0293, U1154, U0110, U029387 and it noted it had lost communication with various Drive Motor Control Systems and Hybrid/EV Pwoertrain Control Modules.

So, it was obvious my 12V was dead and I had an under-voltage issue that the various systems did not like seeing inadequate voltage. Off to Toyota to see about a new 12V. Purchased their lifetime warranty model for the bargain basement price of $270. I was assured that replacing the battery would clear the codes and the communication issues and I'd be on my way.

Of course, that is not what happened. I ultimately wound up having the car towed to Toyota. The problem was a bad relay. I should note that I had checked every fuse and relay located under the hood. This particular bad relay was located under the BACK SEAT!!

I'm hoping this might help someone down the road!