I've found that once you hit 9.5 (on a 9.6v pack), you're pretty damn close to the end. If you plot voltage over time, that's where it drops off rapidly.
btw, my 9.6v pack starts at about 11.2v
If you monitored your recording during this test, you'd find you weren't getting signal all the way through to 3v. Also, if you're using a pc, you don't ever want this to happen. When the power dies on my UA-5 it causes my laptop to spontaneously reboot!