I just finished my vv passthru for my grand and it works flawlessly. It may not be 100% aesthetically pleasing, but that's not what I was going for. I used a 15v 5 amp input to a lm2596 and put a shut off foot switch on there as well. Potentiometer is accessed with screwdriver and it can go great at ANY voltage. 12v? No problem
it is activated by the reos button, because I used a dummy 18650 (piece of wood) with power going to battery contacts with anode on pos end and flat on neg. hope you like it!
-Sam

-Sam