This isn't a new topic, but to a lot of the newer folks and users it will be. Every battery has three ratings, nominal voltage (in the case of lithium cobalt and lithium manganese 3.7v), milliamp hour (mah or milliamps per hour), and c rating. The first two most people are somewhat familiar with, the last most aren't. Every pv with an integrated controller (which covers every vaporizer Vapor4Life sells except the OMG All Day) also has it's own built in amperage limit. This limit is separate from the battery or cell used inside the pv, and usually lower than the maximum output of the battery or cell used in the pv itself.
There is a heavily used saying that it's not the voltage that kills you, but the amperage. This proves true with batteries, especially lithium based ones. I have never heard of any catastrophic failure from a battery running in usable voltage range (as in 4.2v-3.2v) failing from a .1 amp current draw on it. 3+ amps though is a completely different story. This where the C rating and amp limits of the battery/pv come into play.
C rating- This is the maximum sustained (not burst) output of a battery. It requires only knowing the mah rating of the battery and it's value to calculate. Will give you an example using a few different batteries-
Batt A- 1600mah, 15C= 24 amps
Batt B- 2800mah, 2C= 5.6 amps
Batt C- 3100mah, 2C= 6.2 amps
On protected lithium batts there is a built in protection circuit that shuts the battery down (if working properly) if you try to go over that limit. With unprotected batts there is nothing to stop them on the physical level of the battery itself from going over that amperage limit, which can lead to cell failure. This is why you should never use an unprotected cell inside a pv that doesn't have it's own built layers of protection. Will use two mods Vapor4Life sells as an example- The OMG All Day has no built in controller, only a hot spring to help prevent battery failure. This mod should only use protected cells. The OMG Handle on the other hand has thermal shut off, amp limit, short circuit protection, and reverse battery detection. This mod can use unprotected batts because of these layers. Never use a lithium cobalt unprotected cell though, there is a reason these ship with a protection circuit. Use the "safe" chemistry lithium manganese cells only if you're going unprotected (high drain cells). These batteries have high sustained amperage limits for the 18650 size ranging from 10a-30a, far above that of lithium cobalt.
Amperage limit- Have already brushed on this, now to explain it. Every electronic device has an amperage limit. The outlets in your house, the batteries you use, the USB port on your computer, USB adapter, think you get the point. This dictates how high of a current you can run. This limit works in conjunction with the cell's amp limit on pv's. It's lower than the actual maximum output on the batteries themselves. The OMG Handle is a good example of this. The battery that ships with it is rated for 5.6a maximum output, the unit itself has a 4 amp range limit (3.5-4a, with most being around 3.7-3.8a). This is done so you don't push the battery to it's maximum output. Even if you put a battery rated for 24 amps in it, it won't change what the amp limit of the pv itself.
So how does this affect the vaper? Dual coil cartomizers require a lot of amperage to run, especially the 1.5ohm rated variety. This is why even with the handle you can't push them to 6v if you set it to that. It will supply it the maximum voltage it can within it's amp limit. With passthroughs it's not the pt that controls the power, but the source of power itself. To run a 1.5ohmdc at 5v (that's voltage standard on USB ports, which is why it runs at 5v) you need at least 3.33a of power (this has already been technical enough without me delving into all the aspects of DC cartos). There is no USB adapter on the market from anyone I've seen rated for that kind of output currently. This is why people are having issues using the 1.5ohm DC cartos on the pt.