"Thats 623 hours of playing guitar, if you play 3 hours EVERY day it should be around 200 days(or around 6 months) or TWICE that if you rock 2 batteries. And thats about a good time(especially if you rock out 3 hours EVERY day) to do a major setup and service, witch is a great time to pull off the pick guard and change the battery(if you dont have routed for a battey access)."..... People using 2 batteries usually have them in series. This gives more headroom and changes the sound a little. I like the 9V sound myself. Google it if you re interested, there are threads on it. But that doesn't change the battery life. If the batteries were in parallel, still 9V , but 1/2 the milliamp drain on each, then that would.