If you look at the formatting of voltage and SoC which are doubles too, you might get the idea 
Otherwise there always is this info I like to link to
http://www.cplusplus.com/reference/cstdio/printf/
It is odd that you seem to get worse reconnect behaviour with than without SLEEP_NETWORK_STANDBY. The opposite would be expected and I can't see such behaviour with my G2 Electron, but I can test again with my G3.
I also think that the device came online message is a cloud artefact and not really costing you extra data.