I'm currently using a Zenwatch first generation alongside a Samsung Galaxy S6 Edge on Android 6.0.1. Both devices are always fully updated.
The problem is that when my smartphone is connected to the Wear, the battery of the phone drains a lot faster than when it isn't connected. Since my phone is rooted, I'm using the BetterBatteryStats app in order to keep track of my device, and I noticed that when the smartphone is connected to the SmartWatch, the device almost never goes to the DeepSleep state, with the "Awake (Screen Off)" consuming almost all of the device processing time (this doesn't happen when the smartphone is disconnected to the SmartWatch).
My thinking is that the Notification Listener it's keeping the device from going into the DeepSleep mode, so the smartphone can send the received notifications to the SmartWatch. There's something I can do in order to get a better battery life when my device is connected to my SmartWatch?