Thanks to both of you for the explanations. Batteries make me nervous since I don't much understand the tech, so I'll err on the safe side and go with IMR if I decide to add a Kick.
That good to know...makes sense that the numbers would have some meaning, though that hadn't occurred to me.
Battery Digits: The first 2 digits are the dimension measuring across the battery. The last 3 digits reference to the length of the battery. Protected circuits will add between 2mm and 3mm to the length of the battery.
mAh: The term mAh references to Milliamp Hour.
Protected VS. Un-Protected Battery: The primary difference between the Protected and Unprotected batteries is that the protected batteries have a small circuit board, typically on the bottom of the battery, that stops the charging or discharge of the battery in certain circumstances. Some of the circumstances in which the circuit include: Over-Charge, Over-Discharge, Short-Circuit, and in some cases, overheating.
IMR / ICR:
I = Lithium ion
C/M = Cobalt/Manganese
R = Rechargeable
NiMH:
Ni-MH stands for Nickel-Metal Hydride. Nickel-Metal Hydride batteries have no Cadmium added. Cadmium is hazardous to the environment. When using Nickel-Metal Hydride batteries, charging should be monitored to avoid overcharging. Nickel-Metal Hydride has no Memory Effect and can be charged or topped-off at any time without affecting battery life.
Memory Effect:
Memory Effect on a battery is the loss off run time per charge over the life of the battery. To avoid Memory Effect and attain maximum performance discharge battery completely each use.
Battery Type & Size: Most commonly used batteries in electronic cigarettes and mods.
10440: 3.7 Volts 10mm Wide 46mm Long 350mAh rating.
14250: 3.7 Volts 14mm Wide 27mm Long 350mAh rating.
14430: 3.7 Volts 14mm Wide 45mm Long 650mAh rating.
14500: 3.7 Volts 14mm Wide 52.5mm Long 900mAh rating.
14650: 3.7 Volts 14mm Wide 67mm Long 1300mAh rating.
CR2 / 15266 / 15270: 3.0 Volts 15mm Wide 29mm Long 600mAh, 800mAh, 1000mAh rating.
15270: 3.7 Volts 15mm Wide 29mm Long 600mAh rating.
CR123A / 16340: 3.0 Volts 16mm Wide 36mm Long 880mAh rating.
16340 / CR123: 3.7 Volts 16mm Wide 36mm Long 880mAh rating.
18350: 3.7 Volts 18mm Wide 37mm Long 1200mAh rating.
18500: 3.7 Volts 18mm Wide 52mm Long 1600mAh rating.
18650: 3.7 Volts 18mm Wide 68mm Long 1600mAh, 2000mAh, 2400mAh, 3000mAh rating.
26650: 3.7 Volts 26mm Wide 65mm Long 3200mAh, 5000mAh
NiMH: 4.8 Volts 600mAh
EDIT- In case it isn't obvious I copied & pasted this from another site.