12v battery - is it time to change?

Hi! It sounds like your Prius is functioning well overall, but the 12v battery voltage readings of 9.3-9.8v are indeed unusually low. Typically, a healthy 12v battery should read closer to 12v when the car is off and around 13.5-14.5v when the engine is running. Since your Prius hasn't had the 12v battery replaced since it was manufactured, it's likely due for a replacement. Even though the car is running smoothly now, a battery at that voltage could potentially fail unexpectedly. It would be wise to get it checked or replaced by a professional to avoid future issues.