Firstly, let me say I know the answer to the basic question, but I want to get people's views on mitigating risk factors. In a hybrid tube, generally, the battery should go positive up, so the positive pin on the RDA connects with the positive connector on the battery. The body of the tube is therefore negative and the circuit is only completed if you press the switch, connecting the negative end of the battery with the negative body of the tube. That way around, if there is any unnoticed damage to the battery wrap, the negative side of the battery will connect with the negative part of the tube, completing the circuit and causing an auto-fire situation. If the battery were positive down the polarities are now reversed. The RDA 510 pin touching the battery has become negative and the body of the tube positive. When the switch is pressed, the positive end of the battery connects with the positive body of the tube, completing the circuit. With the positive down, if there is any unnoticed damage to the battery wrap, the negative side of the battery will connect with the positive body of the tube, hard shorting the battery and causing it to immediately heat up with possibly devastating consequences. Now then. If a positive up scenario has a damaged wrap and auto-fires, as long as your build is well within the amp CDR of your battery, all that should happen is a build up of heat generated by a firing coil, and the running down of your battery over a period of minutes. The cotton would soon catch fire, adding more heat. Something in the setup may well get hotter than it should and the battery could overheat. Or if the setup is particularly robust the battery might run down below its cut-off voltage and be damaged, leading to venting. But with the positive down scenario and a damaged wrap, you are hard shorting the battery which will cause it to overheat in a few seconds, perhaps vent, or go into thermal runaway. Am I on the right track so far? So, how do we decide which way out battery will go in the tube, assuming we always check the wraps for damage? I have 3 tubes. One has venting at the top (a CAM mod). No problem with that decision. But two have venting at the bottom and no internal insulation. The tubes in question are a Vaperz Cloud X1, and an AV Able clone. Which way would you put your battery in these tubes? Also, the question of arcing at the switch arises. If there is arcing, it would seem to be more dangerous for that to happen at the positive end of the battery than the negative, would it not? Note: My build is at 0.27 ohms, using a VTC5a battery, so I am well below the CDR for the battery. Lastly, does anyone sell battery insulation tubes that you can put inside tube mods for extra protection?