First, I am guessing that since you had to ask, you probably don't know enough to attempt a build that low, so don't do it until you fully understand super sub ohm builds. So no, it isn't "safe". Now, safety is relevant. A battery doesn't know if you are pulling 25A or 60A or 80A. All it knows is resistance. So we by top end, brand name, high discharge batteries. Sony, Samsung, LG. Basically, on a mech, the battery will run current through whatever wire you stick on it. The trick is, knowing how long you can pulse the battery. The lower the ohms, the shorter the pulse. The 3 battery brands I listed know this and did not even list a "pulse" rate. What they listed is a sustained amperage discharge rate. So you could chain vape all day on a 25A battery as long as your coil was not pulling more than 25A. 0.15 ohm is a good, solid, safe sub ohm build. 0.1 ohm is getting down into the "Gotta know how long you can fire this thing" range. Roughly, 3 to 5 seconds. Always pick the lower.
Lets use a hard short as an example to start with.. 0 resistance, the battery literally runs rampant discharging and heats up very very quickly. This is when you unscrew your mod and get the battery out, and toss it in the bin. It MIGHT still be good, but don't trust in "might". In this case your pulse is crazy high for 0 seconds. It just keeps pumping current across the short.
Ignore any math and ohms law in these examples. They are NOT to tell you how to build and fire a coil, they are only to illustrate amps and pulse time.
Next a 0.1 ohm coil.. say 6 second "pulse". Pulse being the amount of time you can hold the fire button safely. (there is a chart for this someplace, wish I had book marked it)
Next a 0.08 ohm coil. Ignoring math for the example, you might be ok to fire for 4 seconds
next say 0.05 lets say 2.5 seconds.
so we can figure a 0.01 ohm coil will safely pulse for 1/2 second. You better be able to suck in air pretty damn fast to vape on that.
Again, ignore the math. The example was only to demonstrate that the lower your ohm, the faster your battery heats, and safe pulse times (depending on how good your battery is) Which is why.. i say buy only Sony, Samsung, LG.. WE (other vapers) know they are good. Don't use rebranded batteries. Sony sells sony batteries, LG sells LG batteries. They also sell their 2nds to be rebranded as ever-ready (for example) for flashlights or Black and Decker for power drills in the battery pack. (another topic, but those batteries are made specifically to run in series of 4, 6, 20, etc and not intended for single cell use)
Now, all THAT being said.. I am currently running a quad coil, 26ga parallel coil, 10 wraps, coming in at 0.12 ohms. The thing is.. I have to take the battery out after every 2nd pull and check the temp. If it is hot in my hand, I let it rest until it cools. Now, 2 pulls on a mod isnt a lot of vaping. It is a cloud chucking build, so I only need to do 1 pull. (a 2 second pulse, and 1 pull)
Now there is a reason I went into all this information. It is so YOU can go find the battery specs and look for these values. Gotta know what to look for, right? Now, also, unless you are going for clouds on a competitive level, don't even bother with builds below 0.1 ohm. A good 0.2 to 0.15 ohm build will give you any vape you want, really, and it is up to your skill as a coil builder to make the most of that. For example.. Kanthal is a good starter. Nichrome has less resistance per foot than kanthal, so more wraps per ohm, so more surface area so more cloud. Stainless steel is lower resistance than Nichrome, so again, more wraps per ohm. So here is where the skill comes in.. you want your battery to be able to heat the coil. a 1 ohm SS quad core will have an insanely long ramp up, about 2 puffs before you even get any fog. Kanthal heats up much faster, but with a lot less wraps, SO NiChrome would be your best bet in the 0.15 to 0.1 ohm range IF you wanted clouds. Now IF you want flavor, Stainless Steel gives much better flavor than Kanthal or Nichrome. It also glows at a higher temp so even though they may not glow like kanthal, they are just as hot. So for flavor, shoot for a higher ohm build, with a higher gauge ss wire. 26/28 ga SS is good for flavor builds. 28 will heat better. (less ramp up) So.. a really good flavor build would be a 26ga nichrome core, wrapped with 30 or 32ga stainless steel.
See what I am getting at? Custom build your coil to get the RESULT you want. It has nothing to do with how low you can get your resistance to go.
By the way, just an FYI, even a competitive cloud chaser will scrap a coil if it goes below 0.07ohm. I scrap them below 0.09 and usually aim for 0.12 which is still pretty low, but I know my batteries, pulse times, etc etc so I know i can hit that for up to 6 seconds. Sticking to 0.15 or higher avoids the issue (almost) since your can hit it for 8 to 10 seconds, which is a very long pull. (my avg pull is 2.5 seconds, including exhale to pre-heat the coil)
As well.. Boomstick is spot on. It is all about margin for error. Now you might not blow your face off with a top end battery, but ruining a $250 mod hurts almost as much. (V3 flip, gold.. $250.00 usd) *or was the last time i looked up the price.
Google "Mooch's Blog" for more battery information. He goes into great detail on amps and discharge rates, etc etc etc.. He IS a professional battery EXPERT.. as in he gets PAID for doing what he is doing for vapers for free.
Now yes, this post may be confusing. It is supposed to be. Like I said, I want YOU to PERSONALLY find this information and learn it by heart, or at least book mark it as a cheat sheet.
Now my recommendation, is stay above between 0.15 and 0.30 and go no lower than 0.10, That is my vape range, and should be fine for any 5 second pull. Maybe even 7, but who vapes a 7 second pull on a mech? That is for toodle puffers on a cigalike.
Vape within your personal boundaries. Stay within those personal boundaries, and vape safe. AND again.. do not penny pinch on your batteries.
Another point I want to mention, not actually related to ohms...
Is
inspect your batteries when you take them out of the mod to charge them, and again just before you put them into your mod to use, and test the volts. Recharge when your batteries get down around 3.4V (3.2 is the very lowest, but 3.4 allows you a bit of safety leeway)
