Red triangle of death?

My father hasn't drive the prius for over one month, and the red triangle of death and a bunch of other lights are on. So after my father change the battery cells for the Prius, all the lights were gone. However, the red triangle of death pops up for less than 3 secs and then gone. This happens about 3-5 times a day. According to my father, he said that this only happened when the car is going downhill the first few days. He said that it happened when the battery is overcharged. Today, when he drive the car for less than 10 feet, the red triangle of death pops up for a sec again. I used an OBD II scanner and there is no code. Is there any problem with the car and how should I fix it? Btw, any recommendation of OBD II scanner, because I borrowed my friend's scanner.