2006 with 299k miles with a Toyota battery replaced about 100k miles ago. I bought the battery from a good Prius mechanic out of a 2007 customer was parting out and they installed it into my 2006. Toyota battery had been replaced about a year earlier. I've driven it about 85k miles. Been getting catalytic converter P0420 codes for a few years (I just clear codes and drive). California smog check due and it won't pass. Got red triangle for overheating engine. Shop testing indicates head gasket failure. It does burn oil and I may have not kept engine filled adequately and upon examination by shop found the serpentine belt worn enough to not always engage water pump depriving radiator adding to the overheating condition. Belt and pump replaced. Faced with more repairs than I wanted to deal with and too $ to pay for, I bought a 2007 with 160k miles on it. My commute is about 140 miles per day at high freeway speeds. Repair records show a couple of minor oppsies, but nothing major. I am working with someone who may buy the 2006 and will tackle the head gasket and catalytic converter on their own. The buyer knows it is likely I will swap HV batteries. I don't hide things from buyers. I think I know the answer, but should I swap the HV batteries to put the ~100k mile HV battery from the 2006 into the 2007?