I thought it would be a straightforward choice but when I started looking through the forums here I started wondering why folks would choose a flashlight that takes aa vs. aaa vs. 123. Seems like the 123 gives you the most power (I tend to like MORE POWER), but again I am a complete novice.
It's not straightforward at all, I'm afraid. In most cases the CR123s will give you more power, but various drawbacks might not be worth the few extra lumens in the end.
AA vs. AAA
Pros:
— better energy density—one AA holds about 2.5..2.7x the energy stored in an AAA;
— lower voltage sag and better drain handling, which makes it possible to regulate an AA light's output by current—in other words, maintain constant brightness until the battery is fully depleted (usually not done with AAA-based lights).
Cons:
— slightly larger size and cost.
Well, that is pretty straightforward, right? Now let's move on to the 123s.
AA vs. CR123/RCR123
Pros:
— AAs (except lithium primaries) are the safer chemistry—they won't catch fire or pop unless severely abused, and they won't get you into trouble in airports if you're carrying more than a few;
— AA primaries (non-rechargeable cells) are cheaper and easier to procure than CR123s pretty much anywhere in the world, while RCR123s are virtually an online-only purchase;
— low self-discharge NiMH AAs (Sanyo
eneloop line et al.) have much lower cost of energy;
— LSD NiMH AAs self-discharge slower than RCR123s and allow for more discharge cycles until significant permanent loss of capacity (however, lithium-based AA primaries and CR123s have equally low self-discharge that makes even the best NiMHs pale in comparison);
— more convenient form factor—1×CR123 lights are often too short while 1×AAs usually fit the palm/fist comfortably;
— rechargeable AAs have better raw energy density than RCR123s—up to 3.2 watt-hours, while RCR123s are below 2.8 watt-hours. Differences in voltage usually come into play, though.
Cons:
— alkaline AAs will leak if completely drained and left sitting in a circuit;
— 2x to 3x lower voltage compared to (R)CR123s, which incurs unavoidable additional drain and/or conversion penalties needed to boost power;
— (R)CR123s have somewhat higher drain tolerance compared to AAs, especially IMR RCR123s.
— top-capacity AA primaries (
Energizer Ultimate Lithium) can be even more expensive than CR123 primaries—their energy density is similar, though (about 4.5 watt-hours);
— NiMH AAs are rather heavy compared to lithium-based chemistries, which might be noticeable when you're carrying several at a time.
