Each car comes from an entirely different world, with the only common ground between them being that they are using electricity (and sometimes gasoline when it comes to the Volt) to power their wheels.
The SLS AMG Electric Drive starts form a staggering EUR 416,500 (about $565,000) in Germany, while the Volt begins at $26,685 after the $7,500 federal tax rebate in the US, so their owners obviously come from completely different parts of society.
The Stuttgart electric supercar develops 751 hp and 1,000 Nm (738 lb ft) of torque from four electric motors, while the Volt has to live with 149 bhp and 368 Nm (273 lb ft) of torque from its single motor, so they're not exactly similar in terms of power either.
The probability of the two models meeting in the same parking lot and sharing the same electric charging station in Europe is pretty much zero and yet it happened, as the above image clearly shows. In other words, electricity is the only thing these two have in common, but many brotherhoods are formed with only a single uniting feature.