It's been a warm day in Sydney today (45˚ C). Driving home from the shops my alternator reduced it's output voltage, it varied between 12.1 and 13.6 as shown via the OBD2 plug. I was running the AC at the time and had a drink cooler running off the second battery. DRL's were also running. This is the first time this has happened but it was extremely hot in the engine bay. After I let everything cool down, I started the car and the reading was back to normal. Anyone got any ideas, or is it just a heat issue?