(This is actually a reply I drafted in response to EngrPaul's comments about regulation or lack thereof in post #114... been trying to post it as a response for days now, and my system locks every time. Trying this as a Quick Reply instead)
Hi EngrPaul:
Here's why I think a mod with a regulator is a good idea. The problem with alkaline AAA is that, at the relatively high drain rate the Coast imposes, the poor things have just 1/3 the energy capacity of a AA, yet they cost exactly the same. AAA cells are never a good deal financially when you look at it this way. In my humble opinion, AAA cells really belong in 1xAAA light formats where their small size is THE advantage (because operating cost never will be). 1xAAA lights aren't about the power, they're about size and weight and convenience. The problem with the Coast is that it definitely IS about the power, and AAA is simply not an economical cell.
Let's look at hard numbers (capacity numbers drawn from Energizer data sheets and cost numbers drawn from websites popular with CPF'rs).
Name-brand AA and AAA cells tend to cost around $0.40 each. Lithium AA (L91) and AAA (L92) tend to cost around $2.00 each.
The capacity of an alkaline AAA at the approximate drain rate several of us have measured on the Coast is about 0.3 W-hr, and at $0.40 each, you are paying $1.33 per W-hr.
The capacity of a lithium AAA (L92) is about 1.25 W-hr and at $2 each, you are paying even more than alkaline at $1.60 per W-hr.
Now let's assume for a moment that an appropriate adapter can be fabricated to hold a boost driver and a single CR123A. A US- or Japanese-made CR123A can be found online for around $1.75 each and driving the Coast equally as hard as the alkaline, the capacity of the CR123A will be around 3.1 W-hr less converter efficiency (assume 80%) so make that 2.5 W-hr. The cost is $0.70 per W-hr, about half the cost of alkaline AAA. And the cost is even lower still if you happen to have a favorite Chinese CR123A.
Another smart way to go, cost-wise, would be NiMH AAA. Interestingly, a rack of three good-quality NiMH AAA will have roughly 2.5 W-hr of capacity, so runtimes would be roughly comparable to the CR123A mod. (That happens to be how I am running my Coast at the moment.)
But I still like the idea of constant light output that you'll only get through regulation. At build time, you can select the relationship between light output and runtime by swapping sense resistors on the regulator board, which you can't do with direct-drive. And, you end up with the excellent shelf-life and wide temperature range performance of lithium.