Battery sizes and heat sinks

[Knotar]

I've decided to finally build a mod after 8 months and need some help.
First and foremost, there are a lot of battery sizes, and it's a bit overwhelming. Comparison wise, that batteries are similar to a standard size battery? I know people use C battery boxes for 18650 batteries, but are they actually the same size?
Second question is heat sinks. Alot of people use them, alot do not. The question is, as oppose to making one, is there a aluminum heat sink that is small enough to fit on a regulator, that can be salvaged from another device?

 

[jhonutz]

For the first question : C = aprox 18350 so for size of li-ion batts: 18 it`s diameter 35 lenght

Second: Heatsink of what? Probably it`s about electronic PCB heatsink and it`s required for regulators IC.

 

[Killjoy1]

Actually, a C battery is quite a bit bigger than an 18350. A 26500 is the one that is similar in size to a C-size alkaline (26mm diameter x 50mm length)