Wilkey:
As soon as I receive my Doug Speck "A" extenders (a $2 upgrade from his AA extender that won't engage a KL4) I will run 3 @ NiMH A's (I have Sanyo 2400 mAh min / 2700 mAh typical cells) or 3 @ NiMH Sanyo 2100 mAh AA's on either a UBH or a Mclux 3 * 123 body extended by an adapter.
For a super long run time, I could use both of my A adapters and use 3 @ 3800 mAh 4/3 A NiMHs if I didn't feel like running 4 A's.
One could be ridiculous and add a third adapter to run 5 @ A's or AA's.
(Let's see, I have 3 @ 123 adapters coming and 2 @ A adapters. Hmmmmm.......)