Don't have that number, but seriously, I think your supposition is correct. A few more years down the road and they will be even cheaper, as well as lighter and smaller. We are reaching the point where these devices almost become disposable. Plus, bear in mind that the 5 year battery replacement interval is the conservative half life of the battery, per the standards. It's probably perfectly safe to use it after 10 years, certainly after 7-8 years. The batteries in the MicrOFix are essentially composed of modularized CR-123 cells, which we know to have a 10-year life.