The winter temperatures were very low overnight in the area recently, with a low of -8°F/-22°C. When I went to start my 2007 Toyota Prius that was outside that night, it wouldn't start on its own. I ended up jumping the Auxilary 12v battery sucessfully. I believe the battery is original, so around 7 years old at this time. I figured it was just simply time to replace it after this jump was needed. Then I found a video on YouTube that provided a way to check the battery condition. It suggested going into the diagnostic menu to do a vehicle signal check. I did this and my battery was within all measurements noted:
- Under no load battery should be between 12.4v-12.8v = Success
- Under accessory mode battery should be above 12v = Success
- Under full powered on car battery should be between 13.6v-14.4v = Success
Based on these tests, is my battery in good condition and does not need to be replaced? Should I replace it anyways just because it did fail to start my car this once? I was surprised to find out that the Prius auxilery battery is made by Toyota OEM and only a single other manufacturer, and the price is quite high $170-220USD.