The battery life highly depends on the stability of your WiFi connection. A stable connection between your WiFi Access Point and the Crystal Water monitor should yield a battery life of approximately 1 year. An unstable WiFi connection will result in a much shorter lifespan for your batteries as negotiating the connection between the Crystal Water Monitor and your WiFi Access point needs more power than an established connection.
We highly recommend using AA Lithium Batteries for the Crystal Water Monitor.