Am I correct in thinking that I can't use the sleep function to increase battery life on my emontx if I'm measuring voltage?
I can't think of any reason why sleep could not be used. We use delay in the example since we assume if someone is monitoring voltage with an AC-AC adapter they will also power the emonTx with a USB power supply. When using a USB power supply using delay instead of sleep give a more constant current draw which puts less stress on the SMPS.
Ok - It's just that it is commented out in the example sketch:
No I don't think it does. It works ok in the current only example: https://github.com/openenergymonitor/emonTxFirmware/blob/master/emonTx_CT123/emontx_lib.ino
Open-source tools for energy monitoring and analysis. This project uses the GNU General Public Licence