Newbie Prius owner help.

I've been looking on this forum for a few days and decided to join and make a post. I hope this is posted in the correct section. So I recently acquired a 2002 Prius from my dad. The main battery went out and he let the car sit in his driveway for about two years. He gave me the car for a daily driver recently and I decided to get her back on the road. So, I started with a new 12V battery, which got everything powered up and running to be able to see the codes and so forth. All three main codes were on the dash along with the triangle. So knowing it needed the main battery we replaced it as well. Had the codes erased and reset, car powered up and everything worked perfectly. It shows the batter charging properly and it goes from motor to electric as it should. Ive driven the car for about week now and this morning upon cranking it the triangle came back on with the other three main lights on the dash. The only one lit up RED is the car with the exclamation symbol. But everything seems perfectly fine and it runs perfectly still. My questions is this. The 12V I put in the car IS a cheap replacement, so could this be the issue? The replacement Hybrid battery is a DOORMAN battery with a 3 year warranty. But again everything seems fine mechanically. I'm sure this issue has been discussed but I can find a specific thread. Thank you in advance for any help. I plan on having the car a long time and want to get all of the issues worked out.