I'm looking at the MVS and some other stores varivolt batteries and i dont get it, they say 3-6 volts but when you read on it says it maxes at 4.2volts and also says not to use with DC carto's. I cant figure out how many ohms i need for it. the first PV i tried was one of these and i have yet to run into that guy again to ask him these questions. Also, no one seems to say what carts/atties to get and it doesnt look like it will fit any of my tanks cept my dctank.