In keeping in the battery longevity theme here and here, recently, Don, AB1PH posted to the Yahoo TH-D72 group about some testing he did with primary cell batteries in the BT-15 AAA Holder.  Don compared Everready Ultimate Lithium (L92) batteries, to Duracell Alkaline batteries.

His TH-D72A was set-up to broadcast its location every 3 minutes. The Duracell’s lasted approx. 1h 40 minutes, with the Lithium batteries lasting approximately 7h. By any standard, approximately 4-5 hours is an appreciable difference, in fact that is almost equivalent to the run time of the original battery pack. Sure, they are more expensive, but, I know which I’ll keep spare.