I have a 2009 SR5 with the v6. Yesterday I was driving and I noticed my voltage bouncing between 12.6 and 13.1 volts. No battery light. I did have a large load on it. Headlights, A/C full blast and the fridge was running. I have a Dual battery setup, but both batteries where reading as charged. I did a few hours worth of driving before this started to happen. I'm wondering if the alternator just got hot and shut down to protect it self. I did see this before when I was out west, but it only happened once and worked normally after a minute and never happened again. It has 181K on it. I started it up today and the voltage is normal, starts at 13.8 and goes down to 13.4 after a few minutes. Is this a sign of the alternator dying, or did I just overload it?

Do you have the fridge hooked up to the vehicle electrical system or to one of the batteries directly? Where did you get the low readings from? Was your rig running weird or anything or just showing lower than normal voltage?

Where did you get the readings from? 12.9 is a bit on the low side, but without more context it's hard to say.

What RPM roughly we talking about?

the fridge is wired to the Aux battery and that is isolated by a solenoid when the engine is off. I was reading the voltage from my Scanguage II through the OBD port. Engine was at about 2k RPM and nothing was acting weird. It was just the erratic voltage readings. I have an inverter that has a voltage display that is directly connected to the second battery and the voltage on that was reading what the Scanguage was. Even after turning everything off, radio, headlights, etc, The voltage hovered around 12.9 to 13.0.

I also forgot to mention, checked all the battery connections as well as the engine and frame grounds, all clean and tight.