2006, almost 120k miles...12V Battery or something else (rodents)?

Hi guys...so here's the story, I'll try to keep it brief but include as much detail as possible. Last night I stopped at a grocery store to pick some things up. I have a base package 2006 Prius (no smart key), so I always lock my door by using the fob button. When I pushed the button, nothing happened. Confused, I opened the front door and tried locking it with the automatic locks on the side door...still nothing. I plugged the key fob into the slot and pushed power, nothing. The green light on the power button was blinking. I also noticed the lights in the cabin were pretty dim.

After a few mins, the security light started flashing (as it normally does when the car is off). I tried a few more tries and the car eventually turned on, but the red triangle was on. The clock was reset to 1:00, but if I remember correctly, the radio stations were still programmed, or at least it was on the station when I turned off the car. At this point, I decided to drive it to the dealer (a few miles away).

They said they were getting some kind of odd error code. Something to possibly do with the transmission, but they weren't sure. They said it could be some rodent problems, as some wires seemed like it could have been chewed. I thought it was the 12V battery, since all the symptoms were there (key fob not working, dimmed lights). Also, my MPGs have been below 40mpgs recently, I normally average in the low 40s since my commute time to work is only about 10 mins.

The dealer kept the car overnight to see if the charge on the 12V this morning would be low, since it may have charged a bit while I was driving it over last night. I just called them and they said the charge was fine, so they're continuing to diagnose the problem.

Any idea as to what could be the problem? I've noticed no problem with the transmission (or whatever the Prius uses). The only thing I've really noticed is the lower MPGs (I think it's sitting at 39.0 right now) and a slightly louder engine when I accelerate (especially on the freeway). The 12V is the original, as I have not changed it since I bought it new in 2006.

Any troubleshooting help is appreciated!

 

I just got a call from the dealer and it is the 12V, so they're going to replace it. They said it continually needs to be recharged. The good news also is that there is now wire damage due to rodents. Phew!