Red Triangle after 12v battery replacement

I just got my 01 prius back after a month of not driving it. I lost all my keys and had to get the ecu replaced at the dealership and they replaced my 12v as well because apparently the one the previous owner had in the car was aftermarket. I just got the car back three days ago and its been driving totally fine since then but the red triangle came on when I was driving home this morning. I pulled over and checked under the hood and checked under the car but nothing looked seriously wrong and I didn’t notice anything wrong with the way it was driving. It was only less then a mile back to my house so I just drove it home carefully, nothing seemed wrong with it on the drive back. Called the dealership and they said they would read the codes and fix it if it was an issue with the battery but when I went to take the car in the warning light had gone away. It had been about 3 hours since it came on at this point. Is this likely an issue with the battery or could it be something thats come up with the car sitting so long? I dont think its the hybrid battery because the one in this car was replaced before i bought it, though i dont know at what mileage. Ive been paying attention to the hybrid battery display the past few days and it seems to be acting normal. Should I keep driving the car until the triangle comes back on and they can read the codes? Any ideas on what the issue could be?