Stick to brand name batteries.. Sony, Samsung, LG and avoid rewraps. Especially avoid any battery that list a "pulse rating". Sustained Amp draw and MaH is what you need to know. Samsung 25R are pretty much the go to battery for mech users. If you have an issue, like a hard short, those batteries will vent all the way to 0 volts. Most other batteries vent, heat, go boom.
As to the build.. I wouldn't use 20 amp batteries on a mech.
As for the build.. it should be safe enough.. at 0.3 ohms on a 3.7v battery (by the way.. always calculate with 4.2 volts as your battery voltage) you will be pulling 12.33 amps from the 20 amp battery at 45.6 watts.
Now the fun part. Look at the question you just asked and the battery you are using. The VGOD is a HYBRID mod. In other words, an advanced mod, for advanced users, who already know the answer to the question you asked. Put it in a drawer and leave it there. Get yourself a nice NON-Hybrid mod. These have a floating 510 pin. What is the difference? If your positive pin is to short, then the negative threads on the atty will contact the + on the battery, instantly causing a hard short. With the samsung battery, you unscrew the battery and drop it in the sink or cat box, or something that wont burn. With a cheap battery it can heat and pop nearly instantly. (a hard short is just like using a 0 ohm coil, regardless of what build you use) I'll give you an example..
a resistance of 0.01 ohm (as close to a hard short as I can get) on a fully charged 20A battery (4.2V fully charged, not 3.7) yields...
a draw of...
420 amps
and
1760 watts.
And if you thought 200w was a hot vape... imagine 1760 hitting your mouth and lungs. Even if the battery didn't instantly explode.
Your safest bet.. switch to a regulated mod until you fully understand coil building. Then get a NON-Hybrid mech and prebuild your coils on steam engine, and pretest the build with the ohms law calculator before even building the coil. Then test the resistance on an ohm meter before you fire it.
MOOCH would throw a conniption fit reading that first post. LOL.
In this case.. your battery is ok for that build, but the mod you are using can be deadly, as it is well above your vaping level. Hell, Its well above MY vaping level!!! (and I am puffing on a 0.07 ohm build right now) Think about that for a minute.. you are asking about a 0.3 ohm build.. I am vaping on a 0.07 ohm build and telling you that your mod is dangerous and that I won't use one... That should scare the hell out of you.
A V3 Flip (or clone) is really nice. It is what I am using in fact.. (a clone, I dont have $250 to drop on a mod, no matter how awesome it is)
https://www.fasttech.com/product/1720900-v3-flip-style-mechanical-mod
It is true that the 510 pin will produce a bit of lag but not much, and certainly not enough to be worth risking your safety for.
Now a lot know I am the first one to scream out about fear mongering, God knows I am outspoken (you don't even want to KNOW what my comments were to this video.. but they were not sympathetic for this kid or his father..
http://globalnews.ca/news/2479197/alberta-teen-injured-after-he-says-e-cigarette-exploded/
I will not candy coat it for you.. that mod you are using is dangerous and above your level. I can tell from the question you asked and battery you are using. That said, if it blows up on you, i will feel badly that you got hurt, but you won't get one lick of sympathy. Just a scolding and an "I told you so"
Harsh, yep. But less harsh than you would be on yourself.. if something happened and you are there with a burned face thinking.. yeah.. he told me, he explained why.. he showed the math, and showed me an alternative and here I am.. face burned and feeling like a jackass.