I'm in my 3rd month of 08 Prius ownership. It came with a 12V battery that starts out undervolt, but is recharged when the car completes its startup-cycle. I know I have to replace ASAP. I use Torque Pro to check for general health, and to record driving stats. Last week, when the heat really got up consistantly above 100, Torque started indicating multiple 'incomplete' tests. Previously, all the Torque tests gave a green check mark. What is odd to me, is that with all these multiple Incomplete Torque tests, not one Check Engine light has appeared. I've read that a failing 12V battery can cause wierd issues. What about high ambient heat? Thank you.
Put your 12v on a charger and it should be able to charge fully to around 13v. Don't worry about Torque readings, just enjoy your car. No warning lights on, you're good to go