What would be the best battery to use in this thing? I am confused 15 amps and 20 amps when I am looking to buy a battery. I want either 2500 mah or 3000 mah, but I just want to be sure I am being safe.
That all depends on what wattage/ohms you prefer to use. If you stay at 50watts or less the VTC6 or Samsung 30Q is ok but the VTC5A is a bit better choice. Over 50watts you want a true 25amp battery in a single battery device. You wont get the higher mAh rating but you will get a higher continuous amp discharge rating.
I vape mostly at 30watts or less so the VTC6 and 30Q is a great battery to use. Im only at about half of the amps required.
Run your build through the Ohm's Law calculators. You can find them online. Input just the watts and ohms. It will tell you the amps required. Find a battery that falls well within that range. The closer you get to the battery limits the harder it is on the battery.