2002 Prius toast? Tons of codes, BAD performance!

So my Prius has had the triangle of doom and later check engine symbols for a few years now. Normally it has codes P3000, B2799, and P3006. Performance-wise, it's OK, except sometimes when I hit the accelerator it doesn't go for a few seconds, then slowly speeds up. Nothing major. I recently took it on the highway and barely made it home! Symptoms included:

1. Triangle, check engine, and parking brake symbol that won't go away regardless of the position of the parking brake (though I could tell it was mechanically working just fine).
2. HV battery fell to 25% on the monitor and engine would NOT recharge it.
3. Engine on ALL the time at high revs.
4. Sometimes engine would work fine, other times it would take a while for it to speed up. When I got to the hill near my home, I barely made it up the hill as the car would jerk forward repeatedly, BARELY making any progress uphill! I barely made it.

Without shutting down the car, I plugged in the laptop and got these codes:
P0300
P0301
P0303
P3000
B2799
P3006
P3009
P3018
P3027
C1259
prius-doomed — ImgBB

I cleared the codes, shut down and restarted the car and let the engine run for a few minutes. Then the only codes were:

P3000, P3006, C1259 (new code).

After clearing the codes, the bizarre emergency brake symbol functioned normally, being on only while the parking brake was actually engaged.

I see those are multiple misfire symbols, but I have not noticed the car ever misfiring before and mileage-wise the plugs are one of the NGK or Denso double platinums recommended for the car. I think they're probably only 30k miles old at most, no way they failed both at the same time!

So was this just a fluke in the computer and restarting it/clearing the codes helped or is it time to retire the car?

 

Should be good. Was replaced a few years ago. The previous one worked for twice as long I believe.

Anyway, I'm being pressured to just buy a new car (too many issues for too many years), so I'll see if it's worth it to troubleshoot this one.

 

The 12V, under suspicion of bad 12V due to strange computer readings (turned out to NOT be 12V's fault; was a bad computer, which was replaced and fixed the problem). I think I'm the third or fourth owner of this car. In between owners it has spent some time unused under the snow for months at a time in used car dealer hands, being juggled between auctions and private used car dealers, and recently has been driven once or twice a week. The weather is very hot and humid here, by the way, which in the past has triggered the orange triangle. Orange triangle would reliably come on in hot weather - a condition that began about 6 years ago. About 2-3 years ago, it reliably started getting the check engine symbol, but the code associated with it was actually a hybrid code. About 1-2 years ago, it started performing badly; I'd hit the accelerator and it would just stand there, but would start to go 3-4 seconds later (slowly). About half a year ago I started getting the turtle symbol occasionally.

As far as I know, HV battery has never been replaced, but again, I am not the original owner. I do know that the HV battery was completely drained at least once about 4 years ago after the 12V was replaced. I was recently getting rapid SOC changes where the SOC would go from 3/4th to 1/4th within a minute or two while the car was parked.

In the most recent drive, when I had the problem, it barely made it uphill. The engine would rattle awfully as the car inched up the hill.

 

I have a techstream knockoff. That's where I got the codes.