With over a hundred battery powered devices I have far more interaction with changing batteries than I would like. As a general rule, SmartThings branded devices have mediocre battery life. My system has a healthy mix of ST and Iris devices. I measure Iris battery life in years while ST devices in months.
I log every battery change and have noted battery life to be fairly consistent no matter how much Motion or contact triggers occur.
ST Arrival Sensor - 3 Months
ST Multipurpose - 6 Months, False triggers after 4.
ST Motion - 10-12 Months
Iris Keyfob - 4 Months
Iris Door/Window - 21 to 24 Months (and still going)
Iris Motion - 19 to 24 Months (and still going)
I suspect the choice of coin cell batteries over CR2 is one significant limitation resulting in reduced battery life.