I've replaced about 30 12V batteries in Toyota Hybrids. Disconnect and replace. In extremely rare cases on the Prius it can require recalibration of the ABS system, but I've never personally experienced this.

 

Thanks for the info. On a funny note I wanted to share with you all what my local dealer quoted me to do the 12V change (called just for grins). $380 for the battery and TWO HOURS labor at typical stealership rates. I laughed and laughed and then the phone went *click*.