I have the scan gauge and i love itmine sits around 13.5 as well. Temp was up to 83 c yesterday but it was 40c out and i was in heavy traffic. Temp hovers between 79 and 81 on a warm day.
Great little gadget that scan tool, shame it does not read the tod error codes.
I found a great Auto elec guy yesterday with a can do attitude so i will see what he can do next week.