Hi, this topic has been addressed before.
In brief, you should use some zigbee repeaters to avoid disconnects. The Keen Home bridge can be used as a repeater.
Also, if you find that your vents are using too much of your battery life (as they poll every minute by default), my Keen Home DTH and jcdevhandler DTHs use a less agressive polling value (every 5-10 minutes for temp/pressure readings) which drastically increases the battery life.
Regards.