Battery drain on a TSTAT can be affected by a few factors:
- Using incorrect, batteries. Alarm.com recommends using high-quality, brand name, alkaline batteries. Sounds like you have done this.
- Not being connected to C-Wire for power will drain batteries quicker. Based on your description, there is no C-Wire, so this may not be an option.
- When Z-Wave communication is poor, the thermostat uses more power attempting to connect to the controller This is a likely cause as the TSTAT has been in malfunction and showing poor communication repeatedly. This issue may resolve on its own so long as the network communication remains consistent.
- Hardware failure. The TSTAT may be experiencing hardware failure causing the batteries to drain more quickly. The only solution for this is replacement.