I got 75 hours with my 9100 w just a regular energizer alkaline battery
Gain on the 9100 was set between 10-11o'clock
11:00 is approximate unity gain setting on the CA-9100. You're not amplifying at the setting you used.
75 hours is way more than Chris says you should get. Perhaps the battery would not last as long if the CA-9100 was providing a good bit of amplification? I think Chris said a good battery would last for 30 hours or so (or maybe it was 40 hours).
Personally, I prefer to use a 9.6 volt rechargeable so I don't need to worry about when to replace the battery.