Not as good as 12AA's in series, but yeah, 12AA's in parralell would give you 4.2 volts fresh and roughly 23000 MaH. I don't don't how the SharkBuck is going to act when it goes into DD. I still like the FiveMega 12AA-3D battery holder scenario better.
I'm not sure what configuration you're discussing. 12AA in a 12p config could get 23000 mAh, if you use 1900 mAh cells, but that would only be 1.4V hot. 12AA in 3s4p would be 4.2V hot, but I'm pretty sure there's no 5700 mAh AA cells about, so you'd get more like 7600 mAh (using 1900 mAh cells).
Either way, a 1900 mAh AA has 1.9*1.2 = 2.23 Wh nominal, so you'd get 27 Wh or so.
Li-ions do get much better energy density; you can put 12x 14500s in a 12AA holder. At 900 mAh, this gets you 39 Wh.
You *could* also dual bore the tube and use 18650's, but you'd only be able to run 6 (3 per column) at the most.
For 2400 mAh, this would get you 52 Wh, but it's a little on the long side -- you'd need some sort of extension, I think. (But you can see bigger batteries are usually a bit better than lots of small ones.)
Another battery option: 5 half-D NiMH. No adapters
or modifications needed in the flashlight. A shrink-wrapped stick of these is what's actually used in the mag charger, BTW. You will need to either charge the cells separately (with spacers in a regular charger), or make a series pack and use a special charger, but the great thing is they drop into a $20 off-the-shelf Mag, not a $100 or so pre-bored one, or whatever the costs & time to get your own host bored. Unfortunately, 1/2D is a niche size, and while there are some cells with truly impressive charge/discharge rates, there seem to be none optimized for capacity, so you get 24 Wh max.
Your 26650 suggestion would probably fit with a cutdown tailspring, but it'd be close (I'm not certain you wouldn't have to shorten the tailcap threads as well, or add a magring). If you do that, you get 54 Wh -- just ahead of the 18650 pack, and no extender or boring should be needed.
But I'd be skeptical that KD is accurately rating the capacity there, so this may be somewhat behind.
Other options for a stock battery compartment, and keeping the voltage up so a buck driver doesn't lose regulation:
- 6xA NiMH, 3800mAh, 27Wh. This won't fit with all "A" cells, but if you pick the right ones, it should. (Needs a special holder; haven't seen one.)
- 9xAA(14500) NiMH, 20.5 Wh; Li-ion, 29 Wh. (In 3x3 holder)
- 4xC NiMH, 6000mAh, 29Wh. Needs a sleeve, and redo the tailcap spring. (I think this might be my pick for this project; actually, the voltage here is close enough you could use a linear regulator, like 8xAMC7135.)
A couple reference points, since I started slinging numbers around:
- A stock load, 3xD NiMH, 12000 mAh, gets you 43 Wh -- only some of the Li-ion configs can beat that for total energy, but its disadvantage is the low voltage, which means you have to use a full buck-boost driver, or tolerate low output through much of its runtime. A 3.6v Li-ion pack (1s?p) has the same trouble.
- Runtime: My 4D P7 uses a 48Wh pack and gets 3 hours 20 minutes before it loses regulation, and maybe 45-60 minutes after that till it falls to half-brightness. My P7 is a 4D mag, running on 4xD NiMH 10000mAh (48Wh), and using 2 4xAMC1735 drivers, so this would scale directly for a 4xC NiMH pack using the same regulator, but you may get better or worse runtime depending on your driver's efficiency, and the drive current used. (e.g., the sandwich you linked has 9xAMC7135 for 3.15 A, instead of the 2.8 A I'm using now.) And using a linear regulator for 1 LED from any pack higher more than 5V is horribly inefficient!
As a side note, 4xD KOH do fine at first in my light, but drop out of regulation almost immediately because they can't maintain the voltage under load (too much internal resistance). So a 4xC config still depends on your driver's out-of-regulation behavior if you want to keep primaries as a backup option; since the AMC7135s act as a (nearly-)direct drive, it still works out OK.
