I just replaced the OE 12v battery in my 2004 Prius at 214k miles (after over 7 1/2 years and it still holds a charge!) with the new "Drop-In" Optima (I paid $170 for it using the offered coupon when it was introduced). I didn't bother to keep the 12v bus powered so I needed to reset the radio, clock, and auto window functions.
One other problem occurred; the AC stopped working!
The MFD said AC off and the steering wheel controls couldn't change temperature. It turned out that some of the electronics got out of sync. I noticed that the steering wheel controls for the defrosters still functioned so I hit the steering wheel AC mode switch which caused the MFD to say AC off. Then hitting the AC mode switch again got everything working again.
JeffD