Gen 2 Prius P0A80 - Options/Advice?

TL;DR My 2005 Gen 2 Prius with ~145k miles on it in threw a P0A80 error code, wondering what my least worst option is.

What happened:

1. On my *return trip* from a nearby grocery store on a hot day, it threw the P0A80 error code (RTOD, vsc, exclamation point). I drove it home.
2. I cleaned the battery fan (it was a little dirty) and cleared the code. Spoiler: this did not fix the problem.
3. I ran a check with Dr. Prius, which said the battery was in bad shape but driveable.
4. Drive maybe 30 miles on the highway with no issues
   
5. The car threw the same error code again (same grocery store, about a minute further down the road, nice comfortable day, highest temp in the battery was mid-80s).
   
6. I spent a lot of time looking at block voltages in Torque Pro while using the vehicle. It looks like everything charges up great, but Block 3 tends to discharge to a volt and change lower than other cells. Block 4 as well, although not as bad. Specifically: Down to upper 14V when the next lowest is ~15.8V or 15.9V. Everything seems to charge up to ~16.9V or lower 17V. The auxiliary battery has read a lowest voltage of ~13.8V, so I don't think it's that, although it was last replaced in 2015.
   
7. When driving after the code, before clearing, the car's battery monitor went from blue to purple rather rapidly, took awhile, and eventually charged back up.

The internet suggests I have a bad module or four. Is it possible that I actually just have a corrosion problem?

My goal is to get at least two more years out of this car (I will be out of grad school by then and have worked long enough that I can get a new vehicle). For funsies I drive to New Hampshire or Vermont or New York for climbing/hiking/whatever.

It looks like getting a proper replacement done (either from NewPriusBatteries or from the dealer) is perilously close to the value of this car (did I mention I'm a grad student?). So I'm considering:

1. Maybe I'm wrong and lucky and there's an easy fix? That's not my life story, so...
   
2. Reconditioning the battery, one module at a time (well, ideally four depending on the charger/discharger I'd beg, borrow, or steal), and replacing the bad ones. I know this will take ages.
   
3. Buying a reconditioned battery from somewhere like PriusKings (there's one a few miles away in Somerville). The cheapest option from them seems to be ~$600 and I trade in my battery.
   
4. Getting a real professional to tell me what's wrong.

I'm comfortable with handy things, although I've never worked with electrical systems.

Am I missing anything? How long should I expect a reconditioning to last? How long should I expect something reconditioned from elsewhere to last? How...driveable is the car with the battery misbehaving? Can I get back to Boston from the middle of nowhere in NH?

 

It's got ~145k miles on it. Relatively low mileage, but also rather old.

 

Yeah I've taken out the battery, disassembled it, decided that I did not want to bother with _owning_ the equipment to do this (I already have a too-small woodshop), and that I don't have the level of interest in doing this twice, and called Toyota.

They took my money for a battery, were all set for me to pick it up, and then...wouldn't release the battery to me. The sales rep (seems helpful, I have no problems with the guy), is being stone-walled by his manager because Toyota considers it hazmat and is enforcing rules they might not have in the past. So...maybe they'll do the labor? Although I'm leaving the trunk disassembled whilst I wait for them to figure that out...

I think they might have a case? The relevant law seems to be CFR 49/173.159 (I am too noob to post links)

I'm not a big fan of any of this but I want to drive this car into the ground and not think about the hybrid battery.

On the bright side I am taking this as an opportunity to add some sound insulation.

 

I opted to have Toyota install the battery. I dropped my car off for servicing and more or less immediately they tried to upsell me (I even got the inspection I declined for free!). I did let them sell me on an alignment and new tires - I know it's a rip-off from them, but I'd had a bad alignment from a local shop, and my tires were a little balder than I'd like. It turns out that this was also the source of most of the road noise. I did have them also do an oil change and transmission fluid change for surprisingly reasonable prices. I did not take them up on the $4000 of other items: serpentine belt for $160 (maybe more? their own service records show the belt replaced at 40k miles ago, so...), spark plugs for $240!, front and rear brakes for $1300, fog light assembly for $800, replacing rotting muffler for something like $700, and some other things that I've already forgotten.

Now here's the great part: they had already sold the battery to someone else! So my car was going to be useless for a few weeks (not that they quoted me a few weeks, mind you. Some overpromising right there...) while I waited. They did give me a loaner at no charge though (literally: they gave me a modern prius with the hybrid battery uncharged). Because of having the loaner I have mixed feelings about the whole experience.

My rear interior was already disassembled so it ended up being ~$350 in labor for just the battery. I wish I had reconditioned the battery myself. At least it would have lasted until NewPriusBatteries had some actual units in stock, maybe longer.

I'll do spark plugs myself because of the age and lack of any records that they've been replaced. My rear brakes are pretty bad (rust!) so I'll do those too, and if I'm feel adventurous I'll look into the front brakes eventually. I figure the car will let me know when my muffler is an actual problem.

Is there an age recommendation on the serpentine belt? The one in my car has around 40k miles and 7 years on it.