Assuming use of alkaline AA batteries to power the emonTH base unit, does the base unit need to be mounted indoors, or ok to mount outdoors if temp above 0degC?
If alkaline AA not really reliable for outdoors for base unit, if I need to have base unit outdoors, is it reasonable to go with Lithium AA batteries, or better to wire in the 5V dc power?
The emonTH is designed as an internal temperature and humidity sensor. It has no special protection that would make it suitable for outdoor use, although I have read of one, possibly two contributors to the forum who have mounted it outdoors, but in a weatherproof enclosure. However, if it’s feasible, my personal recommendation is to mount the emonTH inside on the other side of the wall where you want to know the temperature and use a separate encapsulated DS18B20 Encapsulated DS18B20 temperature sensor - Shop | OpenEnergyMonitor with its cable taken through the wall. Obviously, the second sensor will adversely affect the battery life.
The voltage regulator used in the emonTH2 has an absolute maximum input voltage of 6 V, I didn’t design the unit and I don’t have a bill of materials, but I’m not aware of any other component that might limit the input voltage below this value.
One of the four TH units I have is mounted within the external meter box (the type that sits within the wall) with an additional temperature sensor to the real outside.
Works fine and has been there for over two years on the original alkaline battery. Minimum outside temperature has been below zero, the meter box has managed to (just) stay above.