"While mining for Electroneum, your phone won’t be performing real mining (as is done with a computer), but rather a simulation of mining.

The Electroneum team has described their mobile app as a Mobile Mining Experience.

Instead of actually using your phone’s CPU to solve complicated cryptographic problems (as is done with real mining), the app will continually monitor the available CPU power on your phone. In this way, it will determine the amount of CPU power that could have been used for mining, had the phone actually been mining.

Your phone will then be issued with a hash rate (speed of mining, if you will) based on its available CPU power. ETN coins will be credited to your online wallet based on this hash rate."

So no real mining at all -> normal battery life