P0A80 and P3021 codes, multiple issues, advice needed

Hi All!

So, I have a 2007 with 246k miles. Everything has been great, I'm the second owner, and put about half of those miles on it myself. Only issues I've had were easily remedied - around 200k had a MAF sensor gunked up and got it cleaned. Then the water pump pulley seized and tore up the serpentine belt around 220k. All were straightforward fixes and comparatively inexpensive.

Then this past weekend, went to drive it and got the Red Triangle, VSC, Brake system light, and check engine light, along with error code P0A80. Voltage reading via Torque showed that all blocks read 16.0-16.1 except block 11, which read 14.8.

So, a friend had a spare battery that he had purchased for a flooded Prius but wasn't able to use. I swapped out the entire battery for his, but it was in even worse shape. Voltages were all over the map, and the engine would never even start. So then I put my battery back in - at least I could get the car running with my battery.

On my way home from my Dad's (he's got the garage and everything), had some serious problems. on the way to Dad's I was able to maintain speed with traffic, but on the way back, the car wouldn't get up to speed. The cooling fan ran on full blast non-stop, and it felt like the throttle was stuck around 25%, but mushy, if that makes sense. Then I pulled another code (P3021) which seems to be pointing at block 11 again.

So...to my question(s):

1.) Are my initial findings correct, that it is just block 11 that has gone bad and is causing all these problems?

2.) If so, how reasonable is it to replace just that module? any thing I need to know before doing that?

3.) Is there any chance that I've done damage to other components (the rest of the HV Battery, or the ICE) by driving it like I did?

4.) Is it even worth putting more time and money into a car with 250k miles on it?

thank you guys so much for any advice you might have. I'll be happy to provide any additional info that might help.

 

@davecook89t thanks for the reassurance. I think I'm up for a few rounds of whack-a-mole. my main concern is pouring money into a vehicle that may not be long for this world, but considering the cost v risk seems to point me towards replacing an individual module.

so, next question - is it easier to replace a single module, or to replace a block (since they seem to operate in pairs). I was ok with swapping a battery, as it wasn't really that difficult, but opening up the battery and swapping modules intimidates me a little. just don't want to get in over my head.