The battery life is based on, among other things, self-testing the PLB every month for the rated replacement interval of the battery, which for ACR is 5 or 6 years, depending on the model.
Once a month? I need to re-read my owner's manual, because I could have sworn that the ACR MicrOFix manual stated that the self-test should be limited to ONE self test. ...dashes off to read the manual...
OK, I was confusing the beacon test with the GPS receiver test. Yes, the beacon test is recommended for once/month. (Which means I have been neglecting this test. I will remedy this now.)
The GPS receiver test, however is limited to one test only:
Warning: To conserve battery power the following test should not be performed more than once during the five-year life of the battery pack!
http://www.acrelectronics.com/microfix/microfixman.pdf