Hybrid battery and ECU failed at same time?

The hybrid battery in my 2007 Prius with 165,000 miles is showing all the signs of going out (discharging very quickly, red triangle, etc.) I took it in to a Toyota dealer and had the DTC codes read. They informed me that it was giving codes to replace the hybrid battery AND the ECU. They quoted me about $3,000 for a new battery and around $1,000 for a new ECU.

I am a little suspicious that both the hybrid battery and the ECU would go out at the same time, so I am hesitant to replace both of them. While I am just a layman, it seems more probable to me that one of them is bad and is causing the other to act oddly.

Anyone else had a similar diagnosis in the past?

Here are the codes that came out:
P0607
P3000
P0A80
C0200
C1235
C2300
C2318
B1271

 

Thanks for the tip. I checked the 12V battery and it was indeed low. It hadn't been changed for at least the 4 years I have owned the car, so not surprising. I replaced it today with a new one. Having the 12V battery disconnected reset the DTC codes, but they came back on shortly after.

I've now realized that I will have to go back to the dealer for another $120 diagnosis to see if that made any difference, so instead I have ordered a mini VCI and will re-assess when that arrives in a few days.