until the 9 volt battery cannot supply enough juice.
seriously, though, i do not know how long a 9v in the PS-2 will power the AT853 mics. if i were you, i'd run my own tests to be certain... e.g. get a brand new 9v battery, plug everything up, and set your JB3 to record in MP3 format and see how long the PS-2 will power the mics. if the JB3's hard disk fills up, delete the file(s) and repeat the recording test with the same 9v battery.