[solved - beta electron issue] SLEEP_MODE_DEEP but still using 2,7mA while it should be 0,13mA

Have you seen this thread?

On the Electron you won't need a full Particle.connect() but only a Cellular.on() in order to fully switch it off before sleeping (odd but true - for now).
So you won't see any data/power penalty, since you don't actually connect to the cloud and not even to the cell tower.