Nest Thermostat - Have Blue C wire, why do I still need 2 battires?

[malikriz]

Just bought Google  Nest Thermostat. I see it comes with 2 AAA battires. I have Blue C Wire and already hooked it up.

Why do I need battiresm if I have C Wire? Isn't it the point of having C Wire, so we don't have to use battires and device is powered by C-Wire.

Thanks,

[Patrick_Caezza]

@malikriz 

No, the batteries are there for backup purposes. If there is a power failure batteries will take over and power the thermostat until power is restored or they are depleted. The batteries must be installed for the thermostat to work.