All these batteries make my head hurt, I long for the days of wondering whether my remote takes AA or AAA.....now that i can handle
Mindfield's Quick and Dirty Primer on Mod Battery Types (or: This Won't Be Any Less Confusing):
10440: About the size of an AAA battery. Low capacity, meant for slim PVs like the Precise+ P10.
14500: About the size of an AA battery.
14650: About 1/2" taller than the 14500, a bit more capacity.
16340: A half-size 16650, mainly for stacking or "mini" mods. (Same as the CR123A)
16500: Taller, higher capacity.
16650: Taller still, slightly higher capacity.
18350: Half-size 18650, again for stacking or mini mods.
18490/18500: As the pattern holds, taller, higher capacity. There's no real difference between the 18490 and 18500.
18650: Taller still, slightly higher capacity.
26650: Big fatty, similar to a C cell battery; massive capacity (~4000mAh for standard protected type). Used in the few 26650 mods that exist (eg. Helix, Shockwave)
Chemistry types:
ICR: Lithium-cobalt oxide (LiCoO2). One of the standard rechargeable types, but a bit "safer" chemistry than lithium-ion polymer (the chemistry is harder to ignite and cause a fire or explosion), offer standard charge capacities.
IMR: Lithium-manganese (LiMn). Much safer (though still not safe) chemistry (much harder to ignite), lower internal battery resistance which allows it to discharge more instantaneous current at once, but with the tradeoff being lower charge capacity (about 1/3rd lower than other lithium batteries).
IFR: Lithium iron phosphate (LiFePO4). Like IMRs, a safer chemistry battery than standard LiIon or LiCoO2, but unlike IMRs, have standard capacities and discharge rates, but lower voltage (3.2v).