Resistance doesn't matter. In a regulated box, all of your drain is a combination of two things: the voltage that your batteries kick out and the wattage you set. That alone determines the current drawn from the batteries... ...not the voltage or current going to the coil. Even if the mod shows 3 odd volts on the screen, your batteries are still kicking out their max to supply the power.
What happens here is that the mod first generates the wattage it needs from the batteries. The coil isn't yet a part of the circuit. It will then take that power and swap volts for amps to power the coil as per ohms law. This is why your mod can safely power a .05 even though it needs absurd amounts of current. It doesn't have to get that current straight from the batteries. It can buck it from the extra voltage they naturally kick out when stacked in series.
Your kbox runs two 18650's in a dual-series configuration. This means that fresh batteries kick out ~8v and the cutoff would be about 6v. Your batteries will always kick out a voltage somewhere between these two numbers, regardless of anything else.
With this, we can calculate the current draw for a given wattage at the top and bottom of the batteries' capacity range. The equation is simple. A = W/V
So, at the top of the wattage and battery charge potential, we have 200w/8v = 25A. And for that same wattage at the bottom, we have 200w/6v = 33A. So the max current that the mod will pull under any circumstances is 33A. It can produce much, much more current than this, but 33A is the max it will need to pull from the batteries.
Now, with that in mind, lets talk a little about battery safety in regulated mods. Because current draw is directly proportional to the batteries' voltage under load, the amount of current pulled to get the wattage you choose increases as the charge depletes. At 150w, you start at 20A, but towards the bottom of the discharge cycle, you are going to exceed that.
25r's are generally very stable cells that can take a bit of a beating. It's actually pretty difficult to get them to vent violently, even by hard shorting them. They are widely regarded as some of the safest batteries because of this, in spite of their vanilla 20A CDR. Doesn't necessarily mean you should push them, but it's good for peace of mind. You can be sure that if you respect them, you'll have zero problems.
Gradually exceeding the amp limit is going to shorten their overall lifespan, though I wouldn't call it a very dangerous thing to do. But if you want to get the most out of them, stick to 125w or lower. At 125w, you're going right up to 20A at the bottom of the discharge cycle. If you really want to push that mod significantly past 150w, 30A batteries are highly recommended.
If you just want to crank it occasionally, you're not likely to have any problems. Doing that regularly will, however, take a significant toll on the 25r's. They likely won't vent, but the performance will start to drop off quickly. You'll maybe get a couple months out of them before they're really starting to suck ass. And once they reach that point is when you have to really start worrying about venting. Best to stay as far away from this point as possible...
You can somewhat prevent this by not taking them down to the battery voltage cutoff. Remember, the more the batteries are depleted, the more current they have to give to supply the same power. So maybe try to get into the habit of swapping them above 60% when you crank the power upwards of 125w. That said, you should do so knowing that you're taxing the batteries. It's not recommended. Anything below 125w is a non-issue.
