Two is years. Some people would even say that 1.5 is "years". I go back and forth on this. Is it correct to say that something costs "thousands of dollars" if it costs $1,800? If it costs $2,000, IMO it's clear.
I think most people, when told that something will last for "years", would be quite surprised to learn that it will fail after 2 years.
For example, I have motion sensors in my home and I have to replace the batteries from time to time. If the manual said "the batteries last for years, depending on usage" I would not be surprised if it lasted for 2 years.
Here, it sounds like the battery life will vary greatly based on usage. In fact, it sounds like the battery life is almost entirely a function of how much you use it. It would be interesting to know how much the battery will drain over time if you don't use it, but of course we can't know this for certain before this has been in the wild for years.