i just got a 9v 8000mah battery from b & h photo and was wondering the duration of one charge. i recorded a band Friday night for roughly 2 hours and 15 minutes. on Sunday i set it back up and recorded the tv for another 5 hours and 10 minutes before it shut down. i did not charge the battery any since before the band Friday night. i can conservatively say i can go 7 hours on this one battery.
all this while running my mini mp and tascam hd-p2 from the same battery. i highly recommend this battery.
http://www.bhphotovideo.com/c/product/480307-REG/Impact_BPD8000_BPD_8000_Universal_Portable_Li_Ion.html