I just had to change the battery for the 2nd time last week.
I have been using the sensor for just over 4 years.

My usage: approx. 1-2 hours / week.

After use, I wash the sensor briefly and dry it. It is then stored separately from the belt.

In my case, the battery lasts for over a year, depending on how often you use the belt and, of course, that you disconnect the transmitter from the belt after use and dry it.