I use just the UMC. I don't even get close to using up the range of the car in a day unless I'm going out of town on a trip, so it stays hanging up on a wall hook in the garage. I go on trips maybe 4 or 5 times a year, so then I'll pack it up and bring it with me. I also use less than 40A for charging. Hank Lloyd Wright was rather hot under the collar to tell people in bold that 40A is perfectly fine all the time, but he was focusing on if the circuit is properly wired. The concern I have is on the other side. If a piece of electrical equipment (the UMC) is listed to handle a maximum of 40A and is a bit warm at that level, why push it to the maximum it's rated for all the time? I use 31A, so I'm not constantly pushing on the maximum capability of what it's rated for.