My HP LV Evo is 3.7v so I am not using 6v in the ultra, or have not tried 6v in the ultra anyway. I prefer not to stack cells if at all possible. Battery life is decent with the AW 14500 IMR, I can get 4-5 full, decent hits before the entire ultra is too hot and needs a cool down. I usually change batteries once they get past the point of feeling a good solid charge. I found with the Evo, it can still get pretty hot, but if it's not getting full juice, it won't vape as well, it will feel hot, but just won't get quite up to vaping temp, so it has a point of no return once the battery starts to sag. I find I can load it, hit it 4-5 times while it's warmed up. Let it rest, try to go back for a few more hits, but if it starts to get warm but not hit easily, I will simply change the battery, and keep going. If I stuff the chamber pretty full, I can usually go through 2 batteries to finish off a load. Now this isn't ideal long term use, this is for quick tokes when trying to be very stealthy, or when I am waiting on another vaporizer to get up to temp (cloud) and have a bit of a wait, I might toot on it a few times.**I'd like to repeat again that my ultra has a sleeve of high temp soft silicone tubing, and a patch of grip tape as a thumb pad, to help protect my hand from the heat building up. I can see with out it, you will have a heck of a time running the HP LV Evo on there and being able to hold it for long.
I am still having some combustion at the start of the load, when everything is fresh, including battery. It is a fine hair line, getting this HP LV core started, but once I get it going, I usually get decent vapor using long, med. speed pulls, Noah style. I am still working on the technique of starting the load with out combusting a little, you only get one shot at it each time, and so far, I keep missing my mark. It's hard to feel the hot air at first, and on a fresh charge, it gets hot really fast, as it makes its way through the fresh load. Since you rely on feeling that to determine how hot the inside chamber is getting, and also taste, it doesn't leave much room for error. It's a fraction of a second from vapor to combustion when it happens. I am sure in more time I will get the hang of it. I have to be starting fresh and only get the one shot to get it right, so I haven't had that many times doing it yet. I am impressed though at how well it is working for such a small battery. I could see carrying a spare battery or two and having the ability to medicate on the go with a super stealthy sized pocket vape.
If you send yours in to get rewired, I would make sure you let them know you want it set up to run on HP LV on the Ultra. They also sent me a second HP LV that takes longer to get hot, so it doesn't perform quite the same on the Ultra, but does fine on the full size. I would also suggest holding off on sending anything in, until they get this Cera released, they are mighty busy with that right now. Not sure what the turn around for having a core re-wired would be at this point, or even getting a response from CS about having it rewired since I know how busy they are trying to get this Cera ready for release. Hoping that will all be smoothed out in the next couple of weeks. we shall see...