I have 2 electric (pedelac/epac) bikes both of which weigh about 30-35kgms
Since most bike carriers only hold 2 x 15kgm bikes I ended up with a very expensive Thule one. This carries 2 x 35kgm bikes and fits onto the (electric) towbar. I was a bit nervous at first since I was unsure about its capability to lock onto the ball, but I've had no problems so far and I can swing on it and it doesn't budge an inch. Also it tilts which allows the rear hatch to open, but more importantly as I found out trying to use it, its a lot easier to mount a heavy bike.
Bought from Halfords ( had to be ordered - took a day longer than anticipated, but what the heck ) I think you can get direct from the Thule website ( wider choice there ).