I just taped the Dream Theater Toronto show on the one single internal JB3 battery and it was fine. Just make sure it's fully charged to begin with. Double or triple check it... I taped the whole show... exactly 3 hours pretty much, and listened to about 1/3 of it on the ride home before the batteries got really low... the unit still didn't fully lose power though. Eventually I might invest in a second battery, but it's really fine with the first... as long as you aren't moving too much. Oh, and keep the volume for the headphones turned down to zero and either keep the backlight on 3 sec or turn it off completely if you can.... i just got my JB3 recording and after quickly checking the levels... (note: for DT, i kept it at gain of +11db for the whole show) just locked the players buttons and stuck it in my hoodie pocket.. didn't look at it again until the intermission, where I started a new file and did the same thing... It worked out really nicely.