How many times are we told to replace batteries when we change the clock? Given my profession I have seen the benefits of smoke detectors as well as the tragedy which can occur if smoke detectors are not working.
To my surprise modern detectors from Kidde and probably other manufactures have 10 year batteries. In 10 years just throw it away and get another. Cost when amortized over 10 years is less than the cost of 2 batteries each year.