M19 low battery code very low battery power

[davidwiseman461]

 The batteries were just replaced, new batteries tested with volt meter before install  indicate 1.7 volts.   Batteries that came out showed 1.5 volts on tester. 
checked wiring on unit the dissplay shows 

Y C W G R all connected

Power info screen indicates 

VIN 39.055 which varies up and down a bit. 

what should the VIN reading be?

how do I test if I have power coming to the thermostat with my tester?

I only use thermostat for heat only which works fine, my concern is it will go off line?

[jenniffert]

Hi davidwiseman461,

Thanks for posting in the community! I understand that receiving "M19 low battery code" and "very low battery message" can be concerning. I also know how important it is to have your system and thermostat working correctly after replacing the batteries. I'm here to help!

To better investigate the inconvenience, I'd like to ask the following:

• What is the model of your Nest thermostat? Here’s a helpful article about how to identify your thermostat model.
• Would you mind sharing a picture of your current wiring installation?
• When did you install the thermostat?

Regarding your questions about the VIN values, the values for Voltage Input (VIN) typically depend on the thermostat model and whether the system is active or not. However, these values can fluctuate slightly. This voltage is the electrical current that flows through the wires. For more detailed information about power values, please refer to this article: Nest thermostat information menu.

In addition, to test the power of the wires, you may need a voltmeter or multimeter to check the voltage of each wire. If you're unsure how to do this, I suggest you contact a Nest Pro technician or a technician of your choice to measure the voltage.

Best regards,

Jenniffer