100 degree heat, 12V batt low, mulitple Torque test failures, NO CHECK ENGINE LIGHT

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.