What's wrong with the hybrid battery?

Hello there I'm new around here and I need your help

1 month ago I bought a 2012 prius v. When I bought it, the engine check sign was on. There was a catalytic converter malfunction and it still stands.

Since there was a bug problem in the car, I dismantled all the seat carpets, cleaned everything and put it back. While doing these operations, I removed the small 12 v battery because I was afraid of the airbags in the seats.
This is where the problems start. I try to do uber during the day. In the middle of the day or normally, especially with the hybrid battery, when the air conditioner is on, the engine is activated close to the end of the battery, I hope it is charging, and after this vicious cycle repeats several times, the vehicle is literally stuck on gasoline. Sometimes the triangle sign appears, sometimes it doesn't, but the next day it definitely does. When I ask my mechanic, he says that the inverter can get stupid in the heat or the hybrid battery is dead, but I think he doesn't know. I'm tired of constantly removing the main fuse of the hybrid battery, please help anyone with experience. I am trying hard not to burn the car.

 

Greetings again, today the famous triangle sign appeared again. As soon as it came out, I went to a car parts store and asked them to look at the error codes from obd.

In summary, two error codes appear

P0420
P0A80

What are the possible scenarios?
I don't know how to do it at an affordable price.

 

I apologize, it's my fault. 196 k miles
Yesterday, after resetting the fault code, I traveled 150 miles. Sometimes I felt like it was going to be a problem, but so far it hasn't been a problem. But I know that sooner or later it will fail.

 

Last update, my air conditioner was on and my battery was low. I tried to make a fast start at a traffic light and the surprise triangle sign esp brake light all lit up. The brake started to work a bit numb and no matter how much I pressed the gas pedal, it didn't want to go. Same scenario, you see.

Here's my plan
First of all, I want to buy an obd reader compatible with all cars, and a new cat for prius.I would be grateful if anyone can advise me.

The idea of buying new cells and replacing them one by one is crossing my mind, the prices vary between 40-100$ and yes I can easily do this labor myself. But I don't know how many cells there are in total. I don't know how many cells it really consists of? Or I don't know how I can test if there are intact cells in them. In this scenario, which is logical, I don't know how much it would cost an estimated 1000$ to buy and replace new cells.

Or I don't know if I should buy a battery with a 3-year warranty for around 1500$ dollars without looking for adventure.

I don't know what's next after I get rid of the battery problem.

 

While getting information about the car, the former owner said that it had not been used for 6 months and that it was a spare car. Most of what they said was true, new set of tires, new set of brake discs, new brake pads and the car was very smooth on the outside except for the front bumper.He said he changed the battery, but since I have never driven a hybrid vehicle before, maybe he meant the 12v battery, but I didn't understand.

Let me update you on the situation
Yesterday and again today the hybrid system shut itself down and consumed excessive fuel. Since I don't have time, I bought a refurbished hybrid battery with a 2-year warranty on ebay and I am waiting for it to arrive.

In the meantime, I ordered a few parts that I was not satisfied with. I changed the right engine mount, swaybar links and rear wheel balls.

I will manage like this for a while until I earn the money I spent on the battery.