they need the voltage protection removed to run 18v from what I've heard... I happen to run mine at 12v so I'm not certain. but I know a guy who competes in db drag with like 14 of them 16v system that charges at 18v an he's told me personally the protection needs to be removed. he also went on to say it's rather easy to do so he'd explain the circuit to cut should I ever decide to go higher voltage.. nice amps, I'm thinking about picking up two more sometime... I may contact you if I sell some 20" rims I have laying around (a guy is supposed to check them out tonight actually) but I'll pm you an offer if so as I'm not selling the wheels for enough to outright buy the amps...